Video and voice calls

Ability to place and receive video and voice calls

Other changes:
1527008 Fix taking pictures on Samsung phones, #129
c483629 Data race on login, enable stickers, fix sharing images to Tinode
b9954ce Fix broken image preview from camera
d1afd38 Fix toolbar when changing topic avatar
140a046 Fix avatar uploads on signup
e8a1294 Make camera appear in image chooser
f29f841 Fix crash in image preview on very large images
b01957a Fix exception on wrong error class, fix stuck button
8c267d1 Do not unsubscribe from topic in onPause()
d569c50 Hide members list in channels
a9dab81 Crash on null typing indicator in channels
a7cc621 msg.ctrl could be null if connection is already established
6321fe7 Host not updated when switching hosts, race condition on logout
80a5d47 Try to fix a crash due to scaled bitmap being too large
48519a6 Fix crash probably due to Android bug
b7aace7 Add copy function for id
f17cb97 fix for #124
cad8698 Fix for no [submit] button on signup screen
2ce6677 Load local contacts even when offline
0235941 Fix for a crash
5d09e67 Fix crash on unknown MediaType
80d8b98 Get sender on subscription push
c9fb597 Attempt to fix crash on missing drawable
cb4a0db Fix handling of subscription pushes
0581f4a Replace static listener classes with interfaces (java 8)
e235e51 5a2db3f bd71e8c Fixing launch icon.
c301b70 Added transparent strokeColor to ShapableImageView because its buggy
2fb8957 Dependencies updated, caused breakage fixed
9fecafd Bug fixes

The full list of changes: v0.19.2...v0.20.0