Bug 1127715

Currently Copr only supports projects tied to a particular Fedora Account.
URLs of repositories of these projects contain the account's name.

It might be beneficial to make Copr support projects tied to Fedora Account
Groups, so software projects can have common repos not tied to a particular
developer, but rather to the project itself.

One use case could be this: the sssd project needs a repo to host packages of
some new dependencies for supplying a CI system running builds on already
released distros, which don't have them. Such repos would need to
be added to configurations of developer machines so local CI builds can
install the dependencies.

In case this Copr project owner wishes to stop maintaining it for whatever
reason, the project will need to be re-created under a different account and
the CI server and all the developer configurations will need to be updated,
which is cumbersome and produces service and thus development process
interruption.

One way to implement this could be to provide Fedora account group
administrators a way to select (their own) user or a group account under which
the Copr project should be created on the "Add a new Project" form.

Additionally, to match this change, the permissions system may be extended to
provide a way to grant permissions to groups, but this would be of lower
usefulness as likely only a few people are usually granted modification
access to Copr projects. Otherwise the existing model of granting permissions
to particular users should be sufficient in most cases.