make snippet url friendly

Description

Snippets url are build this way: https://gitlab.com/snippets/<id>

Given a snippet url, you can't really tell which snippet you reference.

Proposal

Snippet url could be built this way: https://gitlab.com/snippets/<title_slug>

That would make it more readable when used in a Dockerfile for example:

Compare

FROM alpine
ADD https://gitlab.com/snippets/2/raw

with

FROM alpine
ADD https://gitlab.com/snippets/custom-entry-point/raw