Introduction of a new "About application" page

+ version number from Manifest
+ urls for license, list of changes, support
+ based on concepts as found in https://github.com/schildbach/bitcoin-wallet
+ theme-aware page (dark/light design)
+ returns correctly from web pages (like source code, support forum) to the About page
+ (C) 2014 Open Whisper Systems
+ obeying code style guidelines