BugFix Canvas Metadata blank for new canvases #125

- Add workarea::have_meta_data with minimal test presence of grid_size and grid_show
- Create from default value if no have meta data
BugFix #540 - Metadata panel do not update 'snap' values
BugFix #493 - Press remove metadata button crash if no document exists.

- add action group to meta data dock
- meta data toolbar done over action_group
- use action_group set sensitive into changed canvas view
Merge pull request #92 from d-j-a-y/djay_metadata_fix

BugFix(s) Canvas Metadata
MicroOptimize on closing canvas

- multiple find_canvas_view call to a variable
Fix "KeyframeActionManager::refresh(): Not ready!" message

- In changed_canvas_view_vfunc change call to ::Refresh by ::Clear (based on dock_layers)