If the user disables an account, this saves it so that on any
subsequent start-ups, the account won't be connected until the user
explicitly re-enables it.
ProtocolSettings were reworked to allow for publicly loading/saving
settings from BMessages, rather than solely from BViews.
In addition, all program-side disabling, enabling, and toggling of
accounts has been consolidated into ProtocolManager. This makes life
easier for other parts of the program that have to do these things
anyway.
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