Depending on the state of the Flarum installation (installed, not
installed, currently upgrading, maintenance mode), we should enable
different sets of service providers.
For example, during installation we should not resolve a setting
repository from the container. This new architecture lets us do so,
but we can easily (and cleanly) register a different implementation
during installation.
This should prevent problems such as #1370 in the future.
This finally adopts the new standardized interfaces instead of the
work-in-progress ones with the `Interop\` prefix.
Since we have now updated to PHP 7.1, we can also use Stratigility
3.0 as the middleware dispatcher.
This prevents garbage collection to randomly break the installer:
before installation, the models that are being accessed have no
database connection.
Now, the middleware is only mounted into the forum's middleware
stack. I want API requests to have stable performance, and the
forum middleware stack is only mounted when Flarum is installed.
This class holds all information relevant to a local Flarum site,
such as paths and local configuration. From this information, it
is able to instantiate a Flarum\Foundation\Application instance,
which represents a Flarum installation's runtime.
This will also be useful for setting up e.g. multi-tenant
environments.
The various middleware can be registered in the service provider,
and the rest of the logic can all go through one single front
controller (index.php in flarum/flarum, and Flarum\Http\Server in
flarum/core).
This will also simplify the necessary server setup, as only one
rewrite rule remains.
