Add option to rename repository

[BTWS2]

trafficstars

If users make a typo or want to change the name to a better one, there is no option to do so currently.

~~Bart noted that the repo name is used as location on the server. A rename on the website should result in a move in the file system.~~

[chvp]

Note that the name being used as a location is no longer true, so this is not a problem.

[BTWS2]

Solved by #4381.