Tksheet

Addressed:
- [281](https://github.com/ragardner/tksheet/issues/281).

Fixed:
- [283](https://github.com/ragardner/tksheet/issues/283).

Fixed:
- [282](https://github.com/ragardner/tksheet/issues/282).

Fixed:
- [280](https://github.com/ragardner/tksheet/pull/280).

Fixed:
- Find in selection would sometimes fail.

Improved:
- Redraw optimizations.

Fixed:
- 7.4.12 deselection display regression.
- Header and index dropdown boxes with center aligned text made text spill out of the cell a little.

Improved:
- Further minor redrawing performance improvements.
- Minor tree build performance improvement.
- Minor performance improvement for moving rows/columns.

Addressed:
- Edge case error with moving rows while using treeview mode.