add homepage with activity summary

[maciejBart99]

I would like to see a home page, after login, with the summary of recent activities and notifications like:
-PRs to which I am signed as a reviewer, and somehow mark those which are waiting to long
-My PRs which are waiting for a review and and those which has been reviewed - in general, my PRs statuses
In future it would be a perfect place to put things like my personal statistics as a timeline, or other information, notifications, etc