scide: introducing restore function

The restore feature saves constantly into temporary files modifications from
user. In case of Supercollider crash, It offers to the user the ability to
restore unsaved modifications.

The temporary files (*.bak) can be found into the Supercollider config dir.
scide: restore: delete all tmp files when discarding change

This patch makes sure there is no tmp files left when exiting SuperCollider and
discarding all changes.
scide: restore: add coalescing

This patch avoid to store tmp files at each document edition. It sets 100
modifications or 60 secondes of idleness before storing the restore tmp file.
scide: restore: use tmp folder into SC config dir

This patch lets restore feature to use its own folder into the SC config dir.
Merge pull request #1267 from vdonnefort/scide/restore

scide: introducing restore function