This way the forum and private group client do not need to keep track of
message timestamps themselves and do not need to interact with
post/message factories.

Fixes #373

This commit refactors the code for sharing forums,
so it can be used for sharing blogs as well.

It does not yet include code for responding to blog invitations.

Closes #517

This allows for swiping left/right to read other posts by using
a ViewPager.

This hasn't been done as a separate activity, but with
fragments, so both can share the `BlogPersistentData` without
needing to reload it.

Closes #428

Clicking the plus in the toolbar open the `CreateBlogActivity` which
allows the user to create a new blog. Only the first identity is
considered, but support for more identities can be easily added later.

The actual list of blogs in the My Blogs tab will be done in the next
commit.

Switched AppBus for ResultHandler, Controller for Helper. Added the basics for LifecycleControllers and implemented it for BriarActivity and NavDrawerActivity

This changes `ShareForumActivity` to use two fragments to facilitate
forum sharing with the new Forum Sharing Client backend.

The `ContactSelectorFragment` allows the user to select a
number of contacts. If there is an ongoing sharing session or the forum
is already shared with the contact, it is disabled in the list. If there
is at least one contact selected, a button appears in the toolbar that
brings the user to the `ShareForumMessageFragment` where the user can
write an optional message to be send along with the invitation.

After sending an invitation, the user is brought back to the forum that
she shared and there is a snackbar showing up briefly to indicate the
successful invitation.

The invitation is shown along with the message within the private
conversation of each contact. The person who shares the forum also sees
the invitation and the message as outgoing messages that also display
the current status of the messages.

A notification is shown like for other private messages as well.

Please note that this commit does not include a way for users to respond
to invitations.

Will currently fail at runtime; requires a public key and a server onion.

Show system notification for successful introductions

Modified the project structure, removed module extension and went instead for a non-complete core dependency graph

Semi-encapsulated the core/api dependency graphs and created a proper structure to load eager singletons