Add Gitlab template

[mspaulding06]

Hello,

I'd like to add a simple template for projects hosted on Gitlab. I've added a couple extras like source file headers and vim modeline support based on information from the Haskell wiki.

[bitemyapp]

A whole template for a repo URL change and some tweaks seems a bit much to me.

[mspaulding06]

If there is a way to keep a local repository of user templates and use them without having to reference the file location directly that would be really great. If I had that then I wouldn't be interested in adding this to the template repository. Do you happen to know if that is possible?

[bitemyapp]

I'd prefer being able to tell Stack to pull (preferably via user stack config) where to find more templates as a git repository URI but I haven't accumulated enough round-tuits for the task and no-one else has either.

I think there's an issue that gets towards this sort of thing, @mgsloan might know more?

[mgsloan]

@bitemyapp Some relevant issues: commercialhaskell/stack#2681 commercialhaskell/stack#1994

[mpilgrem]

I am going to close this pull request since, in the interim, the repository has announced that it is not accepting new templates.