#245 Support for multiple color palettes

[William Kendrick]

Objective

Provide a way for Tux Paint to offer multiple color palettes, which may be switched between (e.g., using left/right arrows on the extreme sides of the static colors -- i.e., the right arrow would appear just before the three dynamic color-choosing options).

For example, a larger set of grays/greys, a set of Bob Ross inspired colors (attached), a full saturation ROYGBIV rainbow, etc.

Considerations:

• An option to deactivate the feature (simplify the UI; revert back to historic single-palette mode)
• A way to specify multiple color palettes via configuration file or command-line option (e.g., "colorfile" could accept a comma-separated list; could multiple "colorfile" options be provided?)
• How would the New Dialog present the additional colors? (concatenate them into one "uber-list"? provide some kind of left/right controls to switch between them?)
• Different palettes will have a different number of colors (the three dynamic color options would therefore have different 'positions')
• How would use of the "colorrows" accessibility option be affected?
• Ensure it works well with the [F4] keyboard shortcut (used to 'warp' the mouse between parts of the UI)
• Ensure it works well with keyboard mouse movement controls
• Decide some good default additional palettes to include (some examples mentioned above)