Since both submitting a command no longer requires a cancellable, and it
is desirable to avoid sending a queued command that has already been
cancelled beforehand, add a new `Command.should_send` Cancellable
property to specify if a command should (still) be sent or not, and stop
passing a cancellable to ClientSession when submitting commands.
Allow call sites to pass in existing cancellable objects, and thus also
add it it as a ctor property to the Command class and all subclasses.
Lastly, throw a cancelled exception in `wait_until_complete` if send
was cancelled so that the caller knows what happened.
Remove redundant cancellable argument from
`Imap.Client.command_transaction_async` and rename it to
`submit_command` to make it more obvious about what it does.
The `SpecialFolderType` was somewhat mis-named, since the special use
does not (in most cases) confer any special type, rather it's simply
defines what a particular folder is used /for/.
As such, rename the enum to to `Geary.Folder.SpecialUse`, moving it in
to the `Folder` class, since it relates specifically to folders, also
rename `Folder::special_folder_type` and
`Folder::special_folder_type_changed` reflect the above and not
duplicate the type name, and similarly rename
`Account::folders_special_type`.
Update the many call sites.
Instead, make the args property a parameter list, and add params to that.
This means Command's serialize method have a different signature compared
to Parameter's, letting us do some more interesting things with it.
* test/api/*.vala: Renamed files that contained mock objects to *-mock.vala,
not *-test.vala.
* test/testcase.vala: Renamed to test-case.vala for consistency, remove
TestCase class from Gee package since that's really not true. Clean up
code for consistency.
* test/meson.build, test/CMakeLists.txt: Split TestCase compilation out
into a separate test lib.
