Transactions for clients

This patch moves transactions out of the database component, allowing clients to perform multiple database calls in a single transaction. This should improve efficiency and reliability, at the cost of increased boilerplate for database calls.

Operations that allow hooks, such as adding and removing contacts, pass their transactions to their hooks. This ensures the whole operation is atomic and isolated, so StorageStatus is no longer needed, hooks don't need to be idempotent, and locks can be removed from clients that were using them for isolation.

This merge request is marked WIP because it will conflict with !74.

See merge request !101

Increase contrast between identicons and background

Identicons currently have a dark or light background depending on the V component of the foreground colour. But V isn't a great measure of brightness - cyan looks much brighter than blue with the same V, for example. This leads to some identicons having low contrast between the foreground and background.

This patch scales the R, G and B components of the foreground colour to 3/4 of the full range and sets the background to white, so there's always good contrast between the foreground and background. The patch also adds a 1dp outline around identicons and adds some padding to the identity selection dropdown.

Before:
![device-2016-02-10-150200](/uploads/2456ff047d4d33b4537f3489c9018679/device-2016-02-10-150200.png)

After:
![device-2016-02-10-154634](/uploads/758c71e3c160e0f9fc50a507323daa7f/device-2016-02-10-154634.png)


See merge request !100

Psycho killer, qu'est-ce que c'est?

Use message validation hook in forum sharing client

This patch moves the forum sharing client's update handling from an event handler to a hook to ensure the update is handled even if it arrives just before shutdown.

See merge request !99

Allow messages to be deleted.

Fixes #238.

See merge request !98

Move subscription updates to the client layer

This is part of #112.

I created a separate client for sharing lists of available forums, as that turned out to be cleaner than using the forum client to manage two kinds of group. The same will presumably be true for the blog and group messaging clients when we come to implement them.

The UX for sharing forums is due to change - instead of sharing a list of available forums with no explanation, we'll explicitly invite contacts to join forums. When that happens, the ForumSharingManager will change but the ForumManager should remain pretty much the same.

When hooks for message status changes have been implemented, the ForumSharingManager will use those instead of listening for MessageValidatedEvents.

When client layer transactions have been implemented, the ForumManager, ForumSharingManager and TransportPropertyManager will use them instead of locks to ensure atomicity and isolation.

See merge request !94

Set category and visibility of notifications. #241

Turns out we can't fully control the visibility of notifications on the lock screen - we can mark them as sensitive, and then a couple of global options determine whether they're visible.

See merge request !96

Fix a couple of bugs in settings

1. SettingsFragment wasn't receiving events because it extended BaseFragment rather than BaseEventFragment
2. Removed broken logic for deciding whether to broadcast a SettingsUpdatedEvent
3. Added the namespace to SettingsUpdatedEvent so listeners can decide whether to react

See merge request !97

Fix crashes, rotation issues with forum posts. #242, #243



See merge request !93

Run hooks when messages are validated

This patch allows clients to respond to messages reliably. Like the hooks for adding/removing contacts/identities, these hooks may be run more than once - that will be fixed when we have client-layer transactions.

See merge request !95