.apply_colors() performance

[wuub]

It's too slow! :-)

diff refresh: http://i.imgur.com/e9A78.png full refresh: http://i.imgur.com/Strkc.png

add_regions() and erase_regions() are called for each one character, making it totaling at 2_ROWS_COLS method calls each refresh. We could check if agregating all regions with the same color eg. "red.default" under a single add_regions() fixes anything.