inveniogc: clean up gc tasks

* Removes obsolete gc tasks (such as bibedit tmp files, bibreformat).
  (PR #1950)

* If CFG_INSPIRE_SITE=1, disables for INSPIRE non related gc tasks
  (BibSword, BibEncode...).

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
inveniogc: guest users gc optimization

* Improves algorithm used to garbage collect user queries generated
  by guests users.  (closes #428)  (PR #1950)

Reported-by: Ferran Jorba <Ferran.Jorba@uab.cat>
Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>