[Tracker] Alternate volumes

[jean-christophe haessig dianosis org]

Hello,

I was wondering if there are any provisions in Tracker to support
alternate volumes. Right now the user's home directory is indexed
by default, and it is possible to add more directories.

However, in the case of a tree that resides on an encrypted volume,
it should be possible to put the index in the root of that tree,
because you don't want an attacker to get data about what is in that
volume.
Similarly, when indexing removable media, users may want the index
o travel with the media, to be readily available anywhere.

In the case of removable media also, the index could be kept in the
main database to enable searching files on offline volumes (this would
be particularly cool for backup archives). However, simple paths shouldn't
be used to locate these files because mount locations are not fixed.

In conclusion, it should also be possible to have multiple databases in
various locations, some of them may be made available/unavailable at any
time. It would also be cool if it was possible to index files in offline
media like cdroms and external drives.