Clean up binary blobs from repo / prevent them from entering

[alfreb]

Some people (no idea who..) have committed binary blobs to the repo. They should be cleaned out. @mnordsletten would also be cool if we could prevent binary blobs from being merged. Can you look into that?

[AndreasAakesson]

So avoid binary blobs from entering seems to be in the progress with #897.

Whats the best solution for cleaning up history? (I belive this issue is related to #266)

[mnordsletten]

I took a quick look at what files in our history are taking up the most space. The sizes are shown in bytes. The largest file here is 27 MB, which doesn't make sense if our entire repo is around 38 MB. I can look more into this at a later time.