Improve performance for PRs and loading of commits page when repo has large number of REFs

Currently when a repository has a large number of Refs (Tags/Branches) we see significant degradation in UI performance, with frequent time outs during platform peak hours. 

Currently Bitbucket supports around 1500 refs without experiencing degraded performance. Any repository that has more than that, will see performance degradation. 

Please help improve performance and support a large number of REFs on repository to improve customer experience and productivity