Filtering entries by committer & issue

[lhaze]

• filtering by commiter: restricts issue & comments by their author, restricts commit by commiter
• filtering by issue number: restricts comments to a specific issue, restricts commits to those which specify this issue

https://github.com/rdev-hackaton/GitHubTimeTracker/blob/f16bdfa/time_tracker/core/usecases.py#L26

Lets move milestone filtering to another issue.