Use cursor cell template when handling 'CSI X' escape sequence
Use cursor cell template when handling 'CSI X' escape sequence

This ensures that the cleared cells are set to the proper background
color, which is the main usage of this escape sequence.

Fixes #612

alacritty/alacritty,jwilm/alacritty,jwilm/alacritty,jwilm/alacritty,alacritty/alacritty,jwilm/alacritty