Release restrictions on project names

Hi,

Description

For now, project names should not contain special characters such as slashes and colons. However, it might be useful sometimes to be able to name them this way, especially since the displayed project name cannot be customized.

Proposal

I am not sure if this is for a particular reason or not, and did not find any previous discussion about this in the bug tracker (except from https://github.com/gitlabhq/gitlabhq/issues/2601 in the old Github bug tracker). I totally understand the difficulties in parsing the URL if such characters as slashes are allowed.

My proposal is then to let the user specify a project name, which will be the displayed project name. This one can contain any character they want, such as colons and slashes. Then, Gitlab would auto-generate a valid URL project name, by slugifying the project name.

Links / references

Thanks!