Implement save/restore cursor state.

Add wxTerminalState structure to group state infos and use it for current and save state.
Add saveState() and restoreState() and use them for setDECMode 1048 (an partial 1049).
Implement using alternate screen and use it in setDECMode 47/1047/1049.
Link DECSET/DECRST 5/6/7/12/25/45 to option setters.

Rename option accessors with real set/get names.