Icons: Scalable replacement for 22x22/Tools.

• Adds 48 vector icons that try to mimic Legacy icon theme.

• Pencil, color-picker and handle-transform are from Inkscape Tango icon theme.

**SOLVED:** About existing icons

**Answer: GEGL stayed, desaturate replaced, measure adjusted**

When I added the icons, there were three conflicts - I didn't replace them, so let's decide now.

Before	After

**Solved**: imperfections and papercuts

**Answer: This requires stylistic changes. This should happen in a separate MR.**

Some of the icons would gain from additional improvements - but this can be done later. In my testing they looked good enough

A few icons have visible style change (thinking of gimp-tool-ellipse-select in particular, tweaked colors, shadows and corner radius). In my opinion it is an improvement. If you find some change you're not in fond with we can discuss and change this!

@cmyk.student feel free to add changes so that the icons are actually connected with the code.

Fixes gimp#887 (closed)