information: add support for about, help and licenses

add screens to the main information screen for displaying:
    about screen
    license screen
    help screen
these fragments load html files from assets.

for now just adding the license screen until the other ones are ready.

remove help entry from preferences and replace with version informations.

also some little cleanups, as always :P

Change-Id: I0f5811a422d177081c683a86aac9f753939767b5