Tksheet

Fixed:
- Drag and drop incorrect drop index
- `set_all_cell_sizes_to_text()` incorrect widths

Changed:
- Functions that move rows/columns such as `move_rows()`/`move_columns()` have had their move to indexes changed slightly, you may need to check yours still work as intended if using these functions

Fixed:
- `StopIteration` on drag and drop

Added:
- `gen_selected_cells()` function
- `is_contiguous` to `tksheet` namespace

Added:
- Progress bars

Fixed:
- Fix resizing cursor appearing at start of header/index and causing issues if clicked

Fixed:
- Fix add columns/add rows not inserting at correct index when index is larger than row or data len
- Fix add columns/add rows not undoing/redoing added heights/widths respectively
- Fix add columns/add rows regression

Added:
- Add functions to address [227](https://github.com/ragardner/tksheet/issues/227):
- `get_column_text_width`
- `get_row_text_height`
- `visible_columns` - `property`
- `visible_rows` - `property`

Changed:
- Internal parameter names:
- `only_set_if_too_small` -> ` only_if_too_small`
- Internal functions:
- `get_visible_rows`, `get_visible_columns` -> `visible_text_rows`, `visible_text_columns`, also changed to properties `property`
- Internal function parameters:
- `set_col_width`
- `set_row_height`

Fixed:
- Regression since `7.2.0`: selection box borders not showing for rows/columns

Changed:
- Slightly reduced minimum row height since `7.2.0` change