New features
- WorksheetControlItem: special element, for better UX, while user interact with cell. Now, this element handle drag-and-drop and cell selection (details below)
- Multiple cells selection: now user can select not one, but many sells via Ctrl+LeftClick. Selection also visualizate on control elements
- Actions on selection (first version): now user can apply some actions on selected cells, for example evaulating, deleting, moving.
- Possibility to change result collapsing via double click on '>>>' prompt element
- Add collapsing of text results with a lot of visible lines (limit of collapsing set in Settings). Double click can collapse/uncollapse collapsed text result.
- Drops Python 2 backend.