Fixing problem with comparing char with integer using the <>
operator.  This appears to be happening with some
version(s)/configurations of PostgreSQL but not all.

Added NB_EMPTY_TAPES, NB_DISABLED_TAPES, NB_FULL_TAPES and
NB_READ_ONLY_TAPES columns to getTapePools() query.

The catalogue is now only queried for the tapes of interest.

Replaced Catalogue::getAllTape() with getVidToLogicalibrary()
because only the logical library was needed by the caller.

Fixed

[catalogue] Corrected the slowliness of the RdbmsCatalogue::getArchiveFileToRetrieveByArchiveFileId() method

The RdbmsCatalogue::getArchiveFileToRetrieveByArchiveFileId() method has been modified to return only active (non superseded) files for retrieval

Here is an example:
```
[itctabuild02] ~ (krb5=ctaadmin1)> cta-admin tapepool add --name steve --vo vo_1 --partialtapesnumber 1 --encrypted false --comment "Steve's tape pool"
[itctabuild02] ~ (krb5=ctaadmin1)> cta-admin archiveroute add --storageclass single_1 --copynb 1 --tapepool steve --comment "Steve's archive route"
[itctabuild02] ~ (krb5=ctaadmin1)> cta-admin tapepool rm --name steve
Cannot delete tape-pool steve because it is used in an archive route
[itctabuild02] ~ (krb5=ctaadmin1)>
```

Fixed #816: The group and user mount policy caches of the CTA catalogue are now invalidated when the underlying data is modified

the --comment option

Modified cta-admin to allow a user to not specify a comment

Refactored SchemaChecker

cta-admin tape add does not take a capacity anymore