Unify LogTag

There is now only one LogTag class. The static initializer of
GmailApplication (existing), EmailApplication (new), and
Exchange (existing)  will now set the log tag to "Gmail" and "Email",
respectively. Up until that code is run, it will be "UnifiedEmail".

"setprop log.tag.Gmail VERBOSE" (or .Email, .Exchange) will trigger
all logs to be printed as long as they go through LogUtils,
regardless of what tag is used by that individual log. This lets us
still turn on logging everywhere in one command, but also lets us use
more descriptive tags (like the class name).

And since we no longer have three com.android.mail.utils.LogTag
classes, builds will be much easier.

Also, we now use LogUtils everywhere.

Change-Id: Ib565414fae51d0c3367370db9717aece45f7eb36
20 files changed