Harness (some of) the power of Gradle

For debug builds, if we apply a suffix to the package name, we can
install both the Play Store and debug versions currently.

Also, apply a versionNameSuffix for the beta and alpha releases so that
it is clear which channel one is on.

Change-Id: I7e0d8eca9c2a1fdcf1378ff834471e87cce3c28e
Implement auto versionCode increase

Our version code system is a mess. Let's just auto increase. We'll never
make it the over 2 billion versionCodes that are available so ot should
be okay that we're doing it.

Right now, it seems to also run everytime you resync the Gradle config,
it also increases the version code, but that's how it goes.

Change-Id: I82e70d6cb2b59cb5e33c8bce426b36321d020e25