Tksheet

Fixed:
- Error with `equalize_data_row_lengths()` while displaying a row as the header

Changed:
- Dropdown and treeview arrow appearance to triangles

Fixed:
- External right click popup menu being overwritten by internal when right clicking in empty table space
- Copying and pasting values from a single column not working correctly
- Mousewheel in header not working on `Linux`
- `get_cell_options()`/`get_row_options()`/`get_column_options()`/`get_index_options()`/`get_header_options()` values not being requested option. These functions now return a `dict` where the values are the requested option, e.g. for `"highlight"` the values will be `namedtuple`s

Changed:
- Functions `cut()`/`copy()`/`paste()`/`delete()`/`undo()`/`redo()` now return `EventDataDict` and not `self`/`Sheet`
- `get_cell_options()`/`get_row_options()`/`get_column_options()`/`get_index_options()`/`get_header_options()`, see above fix
- Clipboard operations where there's a single cell which contains newlines will now be clipboarded surrounded by quotechars

Added:
- Functions `del_row_positions()`/`del_column_positions()`
- `validation` parameter to `cut()`/`paste()`/`delete()`, `False` disables any bound `edit_validation()` function from running
- `row` and `column` keys to `cut()`/`paste()`/`delete()` events bound with `edit_validation()`

Fixed:
- Incorrect dropdown box opening coordinates following the opening of dropdown boxes on different sized rows
- Calling `grid_forget()` on a parent widget after opening a dropdown box would cause opened dropdown boxes to be hidden
- `disable_bindings()` with right click menu options such as insert_columns would disable the whole right click menu
- Removed old deprecated dropdown box `dict` values

Changed:
- To disable the whole right click menu using `disable_bindings()` it must be called with the specific string `"right_click_popup_menu"`
- themes `dict`s now `DotDict`s

Fixed:
- Rare error when selecting header cell with an empty table and `auto_resize_columns` enabled

Addressed:
- Issue [221](https://github.com/ragardner/tksheet/issues/221)

Fixed:
- Flickering when scrolling by using mouse to drag scroll bars
- Custom bindings overwritten when using `enable_bindings()`
- Rare situation where header/index is temporarily out of sync with table after setting xview/yview

Fixed:
- Potential error caused by moving rows/columns where:
- There exists a header but data is empty
- Data and index/header are all empty but displayed row/column lines exist

Changed:
- Function `equalize_data_row_lengths` parameter `include_header` now `True` by default
- Right clicking with right click select enabled in empty space in the table will now deselect all
- Right clicking on a selected area in the main table will no longer select the cell under the pointer if popup menus are not enabled. Use mouse button 1 to select a cell within a selected area

Added:
- Functions:
- `has_focus()`
- `ctrl_boxes`
- `canvas_boxes`
- `full_move_columns_idxs()`
- `full_move_rows_idxs()`