Performance test cases

Configuration example
Internal utility for printing time
Initial set of performance test cases

Signed-off-by: Petr Šplíchal <psplicha@redhat.com>
Tag class implementation

New Tag class with support for caching implemented
PlanTags, RunTags and CaseTags containers adjusted
Relevant Tag test cases and create example updated

Signed-off-by: Petr Šplíchal <psplicha@redhat.com>