Revert "IDebug and ServerNameRedirect middleware developed by Pdox"

This reverts commit d4a5ef2ddf4ecbb7955d972d97a7789cf8f22498.

Conflicts:
	esp/esp/middleware/__init__.py
	esp/esp/middleware/servernameredirect.py
	esp/esp/utils/memcached_multikey.py
	esp/esp/web/util/idebug.py
	esp/esp/web/util/main.py
Revert "Removes esp.shortterm."

Temporarily adds back esp.shortterm, just to add a migration to remove
the database tables.  The code itself is still removed.  The app will
have to be removed for good after the next stable release.

This reverts commit d1a1bca4cc50196619bc2dec37b6de7ae04f9aeb.
Removes esp/file_cache/* from .gitignore
Removes icalendar dependency
Removes esp.db.models.prepared