Helper class to reduce client boilerplate

* Renamed BdfReader methods for consistency with BdfList/BdfDictionary
* Added readList() and readDictionary() methods to BdfReader
* Added ClientHelper to reduce boilerplate when converting messages and metadata to and from BDF
* Moved PrivateGroupFactory to the same package as ClientHelper


See merge request !114

Unit tests for ValidationManagerImpl

Unit test for the validation manager. I also changed the way the validation manager loads unvalidated messages - instead of using a single DB task to load all unvalidated messages, it loads a list of message IDs and then loads each message in a separate task. This prevents the DatabaseExecutor from being blocked by a long-running task if there are lots of messages to validate.

See merge request !113

Add contact and transport keys in the same transaction

This avoids a potential problem where the app crashes after adding the contact but before adding the transport keys, leaving the contact unusable.

See merge request !112

Convert BDF types in lists and dictionaries



See merge request !111

Each task is added to the back of the executor's queue, allowing tasks from other callers to be interleaved.

This avoids a potential problem where the app crashes after adding the contact but before adding the transport keys, leaving the contact unusable.

New polling logic for Tor. #250

Poll for outgoing connections each time the network is enabled, then disable polling once our hidden service descriptor has been published. If our contacts do the same, any contacts that are offline when we poll will connect to us when they come online.

This should reduce bandwidth and battery usage. The idea comes from Ricochet:

https://github.com/ricochet-im/ricochet/issues/68

Fixes #250.

See merge request !103

If two contacts publish their descriptors simultaneously, they may both stop polling without retrieving each other's descriptors. Continue polling for 2 intervals after publishing the descriptor.

Poll for outgoing connections each time the network is enabled, then disable polling once our hidden service descriptor has been published.

New polling logic for LAN. #252

Same approach as !104. Modified the poller to cancel any scheduled poll when pollNow() is called and randomise the next polling interval so plugins that call pollNow() at the same time don't end up polling in sync.

Depends on !104. Fixes #252.

See merge request !105

New polling logic for Bluetooth. #251

Increase the polling interval exponentially each time polling is unsuccessful, up to a maximum of 60 minutes. The interval is reset to 2 minutes whenever a connection is made and whenever Bluetooth is re-enabled.

This should reduce battery usage when there are no contacts nearby.

Fixes #251.

See merge request !104

Try to use the real Bluetooth address on Android 6. #225

Fixes #225 until Google breaks the Settings.Secure workaround.

See merge request !109

Don't reschedule the same TimerTask. #254

Also added some unit tests for TransportKeyManager (part of #205). Fixes #254.

See merge request !108

Same exponential backoff approach as Bluetooth.

The polling interval increases exponentially each time polling is unsuccessful, up to a maximum of 60 minutes. The interval is reset to 2 minutes whenever a connection is made and whenever Bluetooth is re-enabled.

Move UniqueId comparator to Bytes for reuse



See merge request !107

Don't communicate with inactive contacts

When we're introduced to a new contact, we need to store the transport keys and start key rotation before activating the contact. During this period we shouldn't use the transport keys for outgoing streams until either the introduction protocol is complete or we receive an incoming stream from the contact, indicating that they've also started key rotation.

See merge request !106

Database efficiency improvements

Some tweaks to the DB schema to improve efficiency:

* Only keep status rows for messages that are visible - this saves space and avoids the need to join the groupVisibilities table when selecting messages to offer or send
* Use adjacent columns for the composite primary key on the settings table

This MR depends on !101.

See merge request !102