README fixes
Fixed jar dependency problems, updated ignores
Temporary fix for broken developer preview of Support Library
Improved handling of signing keys
Signing instructions
Enable building Bote against I2P source

Requires I2P source revision 116c7da67b5bb23b91f9fb55980ceb9865ae7d0a or later
(ie. cannot be built against 0.9.13 source, must use an install for that).
Updated README
Updated android gradle plugin version
Static verification of remote dependencies using Gradle Witness

https://github.com/WhisperSystems/gradle-witness
Show contact pictures in recipients dropdown
Move app initialization out of EmailListActivity so it can be used elsewhere
Separate message to explain why Bote waits for 3 minutes
Ensure that I2P system vars are set in any Activity that uses I2PBote

Sometimes the Android runtime kills off the Bote process to save memory, and
recreates it when the user next opens it. If the user was on an Activity that
was not EmailListActivity, then when recreated the I2P system vars would not be
set, and the first call to I2PBote.getInstance() would create an instance with
invalid paths. This was non-fatal - killing Bote and restarting it would fix
the problem - but was bad UX, because from the user's PoV all their emails and
data had disappeared.
Show number of incomplete emails at top of Inbox