This (way too large patch) enables versioning in config files, and
provides a mechanism by which to load older versions from a newer
version of Geary. It also properly introduces a new v1 config format
that adds several groups to geary.ini to make it easier to read and to
distinguish between incoming/outgoig services rather than IMAP/SMTP.
To do this, a few things that should have happened in seperate patches
were also done:
* Make AccountInformation's imap and smtp properties mutable (they
aren't stateful any more anyway), make ServiceInformation non-abstract
again and remove the subclasses (to get config versioning happening
without an explosion of a classes, it all has to be handled from the
AccountManager anyway), and some other misc things.
ConfigFile is a GLib.KeyFile-like class (and is backed by a KeyFile) that
nonetheless provides convenient a high-level API for getting and setting
grouped config values and asynchronous loading and saving.
* src/engine/util/util-config-file.vala: New ConfigFile class.
* src/engine/api/geary-service-information.vala (ServiceInformation):
Require ConfigFile groups rather than KeyFile instances for loading and
saving. Update subclasses and unit tests.
* src/client/accounts/account-manager.vala (AccountManager): Move generic
account key consts here from Config. Instead of using KeyFile directly,
use ConfigFile groups for loading and saving settings. Rename load and
save methods to be a bit more consistent with the class's role, and
make save_account() throw its errors so they can be reported to the
user. Update call sites.
* src/client/accounts/local-service-information.vala
(LocalServiceInformation): Move service-specific config key consts
here, use new ConfigFile groups for loading and saving.
* src/engine/api/geary-config.vala: Removed, all config consts have been
moved to the classes using them and KeyFile convenience methods
subsumed by ConfigFile.
