Merging of colorpicker implementations. Code cleanup. (See issue #3)

Added `Color` FieldType which allows defining a color directly in the DB config. Eg. `private static $db = array( 'MyColor' => 'Color');`

Updated read me file accordingly.
It's no longer mandatory to name the module folder *colorpicker*. Any name works now.
Cleaned up ColorField class:
 - Removed the `ColorField_Disabled` class, because it's no longer needed
 - Prevent rendering of html tags directly. Instead leverage the underlying mechanisms of TextField. Removed redundant attributes
 - Color of the text is now based on color luminance instead of RGB-average