Add pre and post logout hooks. Should clear subscriptions prior to logging out to avoid mislead flow of activities when reacting to an unknown empty session

Merge branch 'fix/logout-single-instance' of github.com:RocketChat/Rocket.Chat.Android into fix/logout-single-instance

Merge branch 'fix/logout-single-instance' of github.com:RocketChat/Rocket.Chat.Android into fix/logout-single-instance

presenter. Subscribing to each room change on different connected
servers.

[FIX] User status changes when scrolling the sidebar

that the flag FLAG_ACTIVITY_SINGLE_TOP is set to MainActivity when
launching we keep always a single instance of it avoiding it to leak

Hide channel icon when changing server, preventing RoomToolbar from inheriting last seen channel's icon.

Avoids error in case there's no more servers logged in but the app was caught in the middle of connection retry

Logout method does not remove all servers anymore, but instead it removes solely the current hostname which the client is connected

Add remove hostname method to cache; add possibility to set null to selected server, also avoiding a possible NPE

[RELEASE] Increment build version to 38

[FIX] Set app to always use the Push Gateway

Update okhttp version from 3.8.0 to 3.9.0

the issue:
https://fabric.io/rocketchat3/android/apps/chat.rocket.android/issues/59aabd5fbe077a4dcc019902
as refereced by:
https://github.com/square/okhttp/issues/3308

[NEW] Action to upload any type of file