Refactor signal compressor to have better timing properties

• before: emits signals with time range [1.0...2.0] * interval
• after: emits signals with time range [0.5...1.5] * interval

Bascially, now it handles it much better when interval is around
10-20 ms. With the old version it caused KisCanvas2 to drop frames
and look ugly when the user pans the canvas.

CCBUG:409460

1. Conflicts:
2. libs/global/tests/CMakeLists.txt