Created comboboxes to let the user choose a color palette or an interesting location

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Rearranged the layout and made the program's usage more consequent
* Rearranged the layout in a more logical way
* The old image is now translated and scaled in order to give an impression of the new image
* Minor bug-fixes

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>
Implemented some optimizations
* When the new area is only translated, the parts that already have been calculated are used again
* The colors are now saved into an array instead of recalculating the color for each pixel

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>