Issue #174: GeckoEngineView: Release sessions before view gets detached or a new session gets assigned.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1470883

pull request decision task: Do not use gradle daemon and exit with error if no modules are returned by gradle.

This is in preparation for tab support where we will start to switch between multiple fragments (e.g. browser -> tabs tray).
Currently this fragment lives in the sample app. I was thinking to move (partial) functionality back into components.. but
this was too complex for now. I first want to see where this is going and then at the end see what parts can be moved to
a shared component.

Issue #197: Samples-Browser: Create product flavor for different processor architectures and release channels.

Every now and then I run into "out of memory" gradle build errors. Raising the
limit seems to fix that.