Add option to handle text as short message in compose boxes.

When composing a new message the EditText had TYPE_TEXT_VARIATION_SHORT_MESSAGE
unset while it was set when replying to an existing message. The flag usually
results in the keyboard replacing Enter with a Smiley button.

Since some people obviously like having Enter when composing SMS add an option
to change the state of TYPE_TEXT_VARIATION_SHORT_MESSAGE for those EditText
elements.

Addresses issue #646.