Add new multi-select checkboxes to message list

Use the checkboxes of AOSP's Email app.
Use the color chip area as click target for the multi-select checkboxes
Make the color chip area slightly smaller
Added explicit width and height for the new message list checkbox

Without this change Android 2.x does weird things.
Only enable debug logging when running a debuggable build

There have been some complaints from Android developers that get flooded
by K-9's log messages when debugging their own apps. Oops :)
Remove submenu from the account context menu

There seems to be a bug in Android that makes submenus inaccessible on
some devices, e.g. the Samsung Galaxy S2.
https://code.google.com/p/android/issues/detail?id=53239
Don't use extended notifications when privacy mode is enabled