Add colorspace_rgb(), resolution(), and strip() methods (for imagick)

Added 3 methods to the Kohana/Image/Imagick class:

`colorspace_rgb()`
To convert CMYK to RGB

`resolution()`
To change image resolution from 300 DPI (usually uploads) to 72 DPI for web and resample the image (DPI should be `int` or `array` of X/Y DPI).
I've included the option to accept an array with different DPI such as `['x' => 72, 'y' => 96]` if that's your thing ;)

`strip()`
To strip all color profiles and comments from the file (usually another problem with large file sizes)

These have been tested; but I didn't have the time set up proper unit tests for them... :p

Another note; I didn't have the time to implement or even look at the GD driver, and if anything I'd like to work on a GraphicsMagick driver first... So for now I've got them returning TRUE (please don't hurt me :laughing:)

Cheers