code format and cleanup
All settings were cleared when set shortcuts, now fixed.
Define setting key SETTING_TOOL_CURSOR
minor refactoring
Merge pull request #172 from chchwy/bugfix/tool-cursor-icon

Bugfix/tool cursor icon dissappear
minor
some minor changes for debugging cursor behaviours and pencil settings
Merge pull request #173 from eVoLuTiVeMEDIA/master

some minor changes for debugging cursor behaviours and pencil settings
Merge branch 'master' of https://github.com/pencil2d/pencil
Resolve compile error after merging