Fix punctuation logging

Punctuation is currently put into the same LogUnit as the
following word.  This is counter-intuitive and makes
post-processing more complicated.

This change causes punctuation to be put into its own
LogUnit.

A tricky case is the phantom space.  A phantom space is
inserted right before other text, whose MotionEvents have
already been collected and inserted into mCurrentLogBuffer.
Phantom spaces are handled by creating their own LogUnit and
inserting it into the LogBuffer right before
mCurrentLogBuffer is shifted in.

Change-Id: I102d7cd93982ad37ba0abb6c1ac0f66b85b5f95d