Handle properly repositories in nested GitLab subgroups

[rdicosmo]

Unlike GitHub, GitLab allows to nest repositories inside subgroups at arbitrary depth.
The current regular expression used to detect and extract a repository url from an url on GitLab (or an instance) does not capture that, so one gets a red button and cannot properly interact with these repositories.

For example, see the behavior on https://gitlab.com/litt-arts-num/fonte-gaia/ok-api

[rdicosmo]

Partially fixed in 342d01a : now nested repositories are properly handled, but subgroup pages pop up a red button, because the GitLab API (correctly) reports that those URLs are not for a repository.