Added checks for the size of the interior, cut-out triangle to make sure
everything is drawn correctly at small sizes; buttons are now also
hidden if they overflow from the tool.

- The background selection palette now includes a slider to change the
size of the background grid. Default min/max values are 16 and 64px,
defined in UBSettings. Grid resizes dynamically as the slider is moved.
- Measuring tools' (ruler, triangle) markers follow grid size: 1 square
of the background grid corresponds to 1cm
- Grid size can be different for each page of a document
- Grid size is saved in the .svg
- Documents with a background grid but no specified grid size follow the
default size defined in UBSettings.

Previously, grid size was calculated based on DPI, which can vary from
one OS, computer or display to the next. This new setting allows
documents to be migrated from one machine to another with no unexpected
changes in grid size happening. It also makes it easy to correct any
problems importing old documents (whose grid size might be smaller or
larger than expected when imported on a new version of OpenBoard).

Mostly, removal of old code that had been commented out instead of
removed

Triangle: Resizing of the tool is broken

Now coping creates a full copy of already created item. Copy has it's own content (like video, audio or folder) and stores original item properties (like locked, pos, size, freezed e.t.c.).

It's icon is temporary.

Behavior implemented:
1. Can interact with all items without showing items frames (but ToolBar shows).
2. Cannot move items, but can drag images.
3. Selected items appears deselected when Play tool chosen.
4. Play tool don't requires selecting of item before interacts.
5. Cursor looks like tool icon in text and image widgets (should be the same in any others widgets, but now in w3c is not).

When it rotates with the tool bracket gestures to change its size are not consistent. The parameters of size change does not take into account the position of the bracket.
SANKORE-598
Changing the size of the bracket using the angles opposite the right angle does not work all the time, we must rotate the bracket so you can change its size