Move Activity and Fragment related operations to rx.android.app

This aligns the package name of Android framework classes.
Merge pull request #92 from omo/content-to-app

Move Activity and Fragment related operations to rx.android.app
Fixed broken builds in IntelliJ

To be honest, not even sure how it was building command-line, but now
it's no longer double-including all its funky dependencies.
Merge pull request #102 from dlew/dlew/fix-build

Fixed broken builds in IntelliJ
First attempt at adding Account Observable