Think about removing providers

[sudssm]

So say we have provider A in our system, and we want to remove it for some reason.

Currently, it stays in our user credentials file. So, the next time we start the program, we'll load up A, and then 'repair' it.

The solution is, when the file manager boots up - when we load the manifest - check to see if the filemanager's provider list contains elements that the manifest's provider list doesn't contain. If it does, then we should put these extra providers to the side, and ask the user explicitly if they should be added.

(Keeping the extra provider is actually more than just a ui issue; it causes the bootstrap n (and therefore the filemanager and distributor n) to be smaller than the number of providers we are working with),