Fix cursor position handling when changing column after trigger insertion.
Fix trigger index after insertion in the model side.
Fix target trigger index update after trigger insertion.
Fix style.
Merge pull request #232 from kagu/fix_cursor_movement

Fix cursor movement after trigger insertion
Use a narrow cursor visualisation.
Snap cursor location in trigger row based on mouse cursor distance to trigger borders.
Merge pull request #233 from kagu/insert_cursor

Insert cursor
Add replace mode state to session.
Implement replace mode.
Add replace button.
Select cursor drawing and mouse snapping mode based on the replace mode setting.
Clarify names.
Add missing translation to insert cursor positions.
Merge pull request #235 from kagu/replace_mode

Replace mode
Keep target trigger index of the selection stored in session.
Fix trigger index on column change.
Make sheet corner black.
Change column header visuals.
Fix bad idea.