[#1464] Add new property Commit.symbolic_ids.
[#1464] Add new property Commit.symbolic_ids.

Used to query symbolic names, specifically branch and tag names,
asssiated with a given commit id. The property is implemented at
RepositoryImplementation level (default generic implementation is
provided which uses branch/tags cached in the repo object).

Signed-off-by: Paul Sokolovsky <a782451d4c41e36a75176c073353e153afe24dd2@geek.net>

apache/allura,leotrubach/sourceforge-allura,heiths/allura,leotrubach/sourceforge-allura,apache/incubator-allura,Bitergia/allura,apache/allura,apache/allura,heiths/allura,apache/allura,leotrubach/sourceforge-allura,apache/incubator-allura,Bitergia/allura,heiths/allura,leotrubach/sourceforge-allura,Bitergia/allura,lym/allura-git,apache/allura,Bitergia/allura,heiths/allura,lym/allura-git,heiths/allura,lym/allura-git,lym/allura-git,Bitergia/allura,apache/incubator-allura,lym/allura-git,apache/incubator-allura