Evolution kinda sorta supports multiple identities by allowing users
to set up so-called "transport-only" accounts by choosing "None" for
the account type.
Add a CamelStore subclass for those types of accounts so they get
added to EMailAccountStore. It's just a stupid hack to keep another
stupid hack working, but this should sustain us until we can support
multiple identities FOR REAL.
These libraries are bound for E-D-S so they live at the lowest layer of
Evolution for now -- even libeutil can link to them (but please don't).
This is the first step toward moving mail handing to a D-Bus service.
