Adds a user configuration for maximum fps for canvas updates

Under "Performance / Advanced / Limit Frames per Second" there is now a slider that allows the configuration of the targeted frames per second updates the canvas should receive. This configures the updateSignalCompressor in KisCanvas2 to not trigger update events more often. Having a lower fps gives the main thread more time to do other QT event processing, which could be beneficial one some machines/installations.

Differential Revision: https://phabricator.kde.org/D8193