Bug 978587 - Pre: Let Java JARs contain either sources or generated sources. r=blassey
Bug 978587 - Pre: Make geckoview_library and BackgroundInstrumentationTests target android-16. r=blassey

This agrees with Fennec (and BrowserInstrumentationTests).
Bug 978587 - Make GeckoView package org.mozilla.gecko; don't include org.mozilla.gecko.R. r=blassey

This builds a new Java JAR containing only org.mozilla.gecko.R.  This
new JAR file is included in Fennec, but not included in
geckoview_library.  (Usually ant, gradle, or Eclipse arranges to produce
org.mozilla.gecko.R but not include it in the classes.jar output as part
of a library project.  This mimics that.)

Changing the GeckoView package to org.mozilla.gecko declares to
consuming applications that they should produce org.mozilla.gecko.R,
replacing what was removed above (but with correct resource IDs).