Graphics enhancement
Enhancement :
- Fix scale : Scale were a column/row amongst the other, but when there is a lot of columns/rows the scale is hidded or the user have to move the scale using arrows button. Now scale column/row works as a freeze column/row in calc. Pad arrows (not button) still allows to move the scene to hide scale.
- Movable plot items : as the scale is now fixed, plots/views are movable. Items can be moved with the mouse in a drag&drop style.
The mechanics handle add_column / remove_column action and update the view to keep the coherence between items.
Bugs fixed :
- missing left line on imagery item
- Scale label for log views.
Doc :
- add docstring for all items class