app: make GimpBucketFillTool a GimpColorTool.
In particular, it allows to easily color pick. This just makes sense as the bucket fill is definitely what one could call a "color tool", and being able to easily change color without having to constantly switch to color picker tool nor open a color chooser dialog is a must. The fill type option (FG/BG/Pattern) was already mapped to the common toggle behavior key (Ctrl on Linux), which is commonly used for switching to color picker on paint tools. So I decided to remap the fill type switch to GDK_MOD1_MASK (Alt on Linux) to keep consistent with other tools (at the price of a change for anyone used to this modifier, though I doubt it was that much used). I also made possible to combine the 2 modifiers (so you could pick the foreground or background color with ctrl and ctrl-alt).
Showing with 90 additions and 6 deletions