Dynamically update stored credentials in mount config

Instead of storing credentials in a session variable, on login the credentials are used to update any dynamic personal mount points (or create them if system-wide ones are encountered) with the new credentials.

Sharing for `SMB_OC` has been enabled.

The following needs testing:
- [x] iRODS
- [x] Sharing support ~~(this is a little broken at the moment)~~ ~~Separate bug affecting SMB~~ This was a separate issue, fixed in #8293 
- [x] Non-dynamic mount points are working as expected

**21/04/2014** WIP status removed

@PVince81 @icewind1991 @DeepDiver1975