Merge fix on Avatar into develop

Avoid Realm queries for messages with null users

Fix on building the default avatar

Fix crash when building default avatar 

Move logic to the presenter.

Handle odd usernames with dots such as ..., .Foo., .., Foo.. which as causing a crash when building the default avatar image

Merge branch 'fix/filtering_get_messages_flood' of github.com:RocketChat/Rocket.Chat.Android into fix/filtering_get_messages_flood

Handle odd usernames with dots such as ..., .Foo., .., Foo.. which as causing a crash when building the default avatar image

Initial Crashlytics support

Merge branch 'fix/filtering_get_messages_flood' of github.com:RocketChat/Rocket.Chat.Android into fix/filtering_get_messages_flood

this using the newly added ping call without the use of bolts'
callbacks.
Implemented a TaskService class that is used to do the work offloaded
by the GcmNetworkManager which is used here to schedule
keep-alive recurring tasks.