Filter branches by "Merged"

Problem:

1. I go to https://gitlab.com/gitlab-org/gitlab-ce/branches
2. I'd like to prune extra branches by deleting all the branches in the repository that have been already been merged into master.
3. I can't filter by "merged", so I have to go through all 14 pages of branches to figure out which ones can be deleted.

Solution:

I'd like the option to Filter branches by whether they've been merged into master. I know GitLab has the information, the branches that have been merged are tagged as such, I just want to be able to find them easily!