installation: pip requirement version updates

* Updates requirements.txt with specific versions for all requirements.

* Updates mysql-python to 1.2.5 to make it work with the new pip.

* Changes the requirement from PIL to Pillow as PIL is abandoned.

Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
Merge branch 'maint-1.0' into maint-1.1

* maint-1.0:
  installation: pip requirement version updates
Merge branch 'maint-1.1'

* maint-1.1:
  installation: pip requirement version updates

Conflicts:
	requirements.txt

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
WebSearch: timestamp detection fix for empty sites

* Fixes get_database_last_updated_timestamp() so that it would not return
  None in case no records are present in the system.  This solves webcoll
  traceback issues when running on an empty site.

Reported-by: Ole Rønning <ole@tindtechnologies.com>
Signed-off-by: Tibor Simko <tibor.simko@cern.ch>