Currently, a lot of our build variables that are defined at
configuration time, are spread out across the code base, often declared
as `extern` which can break when moving around sections of the code
across files.
This commit introduces a "Config" namespace which basically maps to the
definitions in `config.h`, but allows us to properly access them too
from the Vala source code.
By doing so, it helps us to more explicitly see where we rely on a
build variable from this file (which should be obvious from the `Config'
namespace).
To make it ourselves a bit easier in Meson too, we can declare an
internal dependency, which helps ensure that we pull in the dependency
where needed.
Engine mocks don't need to be in the `Geary` namespace, and including
them there makes it difficult to use them in client tests, so put them
all in their own name-space and corresponding directory.
Move Capabilities to the api directory and make immutable.
Don't pass around out params to simply increment the revision and use a
field in ClientSession, just use the last capability instance. Ensure
after starting a TLS session capabilities are cleared. Add unit tests
for getting both implicit and explicity capaibilities when initiating
a client session.
Move args from open_async to ctor and use these to determine and store
DB file and attachment paths as properties. This allows constructing
the DB instance up front and markig it as non-nullable, simplifies
calling patterns and hence allows removing one use of the deprecated
Engine singleton, and by moving in the local data deletion
implementation from ImapEngine.GenericAccount, also allows removing a
static helper method.
Convert getters that look like properties into actual properties,
remove unused and redundant public and internal API, convert
implementation to use a tree that aucyally maintains references between
steps, rather than each creating a new list of path steps and
manipulating that.
Instead of each top-level IMAP folder being a FolderRoot object, then
children of that being FolderPath objects, this makes FolderRoot an
"empty" FolderPath, so that both top-level and descendant folders are
plain FolderPath objects. Aside from being more technically correct,
this means that empty namespace roots can now be used interchangably
with non-empty namespace roots (addressing issue #181), and custom
folder implementations no longer need to provide their own trivial,
custom FolderRoot.
To support this, a notion of an IMAP root and a local root have been
added from which all remote and local folder paths are now derived,
existing places that assume top-level == root have been fixed, and
unit tests have been added.
