Minor model refactor
 - added "-grouping" to groupings to distinguish structures
 - moved match-grouping into openflow-extensible-match.yang
 - fixed actions structure (list action-list)
 - updated identities bases with "-base"
MERGE AFTER: https://git.opendaylight.org/gerrit/#/c/5109

Signed-off-by: Michal Polkorab <michal.polkorab@pantheon.sk>
Change-Id: Ie2bf3d446f8f5912796bd751e512189d6bf06018