Enhancement : Possibility to resize canvas content during resize

- new checkbox in resize panel
- content is resized using nearest neighbor
- deactivated by default

2 bug fixes :
- remove focus after closing drawer
- fire resize event after undo/redo if size changed
Fix : Fixed styling for resize content checkbox
Merge pull request #175 from juliandescottes/feature-resize-content

Enhancement : Possibility to resize canvas content during resize