[Patch] Add more image filters

[michael2402]

Currently, there is a quite flexible plugin that adds layer filters:
​http://wiki.openstreetmap.org/wiki/JOSM/Plugins/RasterFilters
Although it is flexible, it has no good usability and is pretty complex for quick use.

We have settings in JOSM to change the gamma value (per layer) and deep down in the settings to change the sharpness.

I want to improve the layer filter dialog (visibility / gamma) and add the sharpness value there. I also wrote a new colorfulness filter.

I made some new icons but feel free to find better ones ;-)

Icons are in images/dialogs/layerlist/