Added the enty in the cta.spec.in

This implementation (unfortunately) introduces one more CLI, but
it makes the 0-byte files migration fully independent from the rest.
The main reason is that the query to extract them from the CASTOR
Nameserver is pretty expensive.
The README.md file and the packaging have been updated accordingly.

A previous commit had spun part of the code into a base library, but the split of the library was not helping.
Replaced the cta-lib-base RPM with a cta-lib-common RPM.

cta-migration-tools does not need castor-dbtools, it is sufficient to
depend on cx_Oracle.

Revert "Modified cta.spec.in to avoid problem with official Oracle RPMS not listing libocci.so as a capability"

This reverts commit 8120a9bb.

Revert "Modified cta.spec.in to deal with the fact that that the official ORacle rpms do not list the 64-bit version of the libclntsh.so capability"

This reverts commit c67967a9.

Modified cta.spec.in to deal with the fact that that the official ORacle rpms do not list the 64-bit version of the libclntsh.so capability

Modified cta.spec.in to avoid problem with official Oracle RPMS not listing libocci.so as a capability

This reverts commit 25651a93.

- Added tool to drop from the CTA catalogue all CASTOR tapes from a given tapepool.
  This tool makes use of a temporary table and an additional PL/SQL procedure
  in order to perform efficient bulk operations in the CTA catalogue.
- Made tapepool insertion idempotent.
- Updated documentation.

Now we are also tolerant of whether paths in config file do or do
not have a trailing slash.

Pathnames from the DB must have a leading slash if we have to strip off
the CASTOR prefix, but in any case we will convert all filenames to
absolute filenames by adding the EOS prefix.