Performs some refactoring. Moves UI code out of Log class
and into separate PluginPanel class where all UI components
will be handled together.

Signed-off-by: Jim Teeuwen <jimteeuwen@gmail.com>
Revises the Makefile to add a release and debug build mode.

Signed-off-by: Jim Teeuwen <jimteeuwen@gmail.com>
Further work on plugin UI. Adds log priority icons to the
data grid and finishes implementing the filter text box.

Signed-off-by: Jim Teeuwen <jimteeuwen@gmail.com>