Android: prepare and polish documentation

The Android port is coming along, and so the documentation needs to be integrated and refined.

Things to consider:
-Android doc package: installation, tool support, supported modules, and example.
-links to the pages should be obvious and easy to find (From the reference pages, overviews, Getting Started, and Examples and Tutorials pages)
-make the documentation pages look consistent with other ports or platform pages("Android" to "Qt for Android")
-integrate documentation from wikis into the reference documentation (where it can be reviewed and prevent people from quickly changing it. Also, we don't ship wikis to Qt Creator)