Remove Gibberbot

I have build ChatSecure on Ubuntu 14.04 LTS 32bit. Due to this process I have seen some old entries for gibberbot.

Due to the fact that the aapt file is a 32bit binary I was not able to build ChatSecureAndroid on 64bit.
I have add this information also to this PR.

A detail description how I was able to build ChatSecure on Ubuntu 14.04 LTS 32bit can be find at

http://alword.wordpress.com/2014/05/16/build-own-chatsecure-android-client/

feel free to reuse the information for the Project.