self-serve instances

[wardi]

Add a form for users to request a new instance and have it created for them, instead of requiring that the multisite admin create it for them

[waldoj]

A suggested consideration: addition to an admin-approval process, perhaps permit auto-approval of any request that comes from one of a given set of domain names (e.g., every municipal government in a particular state). IMHO, it's not important that this feature exist at the time of release, but rather that it be possible to later add this feature, perhaps just making this something to keep in mind when creating that approval cycle.