* use the activate/deactivate system from WpObject,
  which allows async activation and error reporting
* drop 'module' property, use 'core' from WpObject

Fixes #20

if there was a remainder in the buffer from a previous iteration,
make sure not to fill too much data and go past the end of the buffer

after consuming the whole buffer, cur & linestart need to
be reset to point back to the beginning of the local buffer

replace them with spaces so that the GVariant parser ignores them

Disconnecting core finishes all pending tasks, which is needed in order to avoid
possible leaks if some tasks are still pending when exiting.

the on_sessions_exported callback runs from within the context
of export_tmp_globals in object-manager.c and when plugins register
more object managers, it modifies the object managers list that
export_tmp_globals is iterating over, making things behave really weird

+ enable the new log writer on the executables
+ enable structured logging in the tests

This is a remainder from the old WpRemote, which is gone.
I would re-add the property, but it's not worth it, since libpipewire
prints it as well by default

In practice we always create a remote and connect to pipewire.
Any other scenario is invalid, therefore, it is not justified
to be confused with so many classes for such small functionality.
This simplifies a lot the modules code.

Also, this commit exposes the pw_core and pw_remote objects
out of WpCore. This is in practice useful when dealing with low-level
pw and spa factories, which are used in the monitors. Let's not
add API wrappers for everything... Bindings will never use this
functionality anyway, since it depends on low level pipewire C API.

If we have properties, strtok will return strings from there as tokens
and the error will appear later as we will attempt to parse an incomplete
GVariant. It is better to catch this early so that we can print a more
useful error message.

So now we can do:
---
load-module C foo {
  "property": <"value">
}
---

The starting brace is still required to be on the same line
as the load-module.

Properties are expected to be a GVariant a{sv} dictionary,
specified in the GVariant text format:
https://developer.gnome.org/glib/stable/gvariant-text.html

This is a cleaner way to interface with the remote pipewire daemon.
The WpRemote base class can be subclassed also for interfacing
with other daemons (hardware-specific managers, etc)

This is implemented in a slightly hacky way, we register the GMainLoop
as a global object and use it from the module to quit the daemon.
This is bad design because the module assumes it is loaded inside
our daemon.

In the future, this should change. It looks like we should have an
object that tracks the state of PipeWire and main() should track
state changes of that object and decide what to do.

This allows loading of config and modules when deployed in
the target system without setting environment variables.

After discussing things at the AGL May 2019 F2F meeting
and reflecting on the initial design of WirePlumber,
it became clear that it needed a fresh start.

glib log domains are not like the gstreamer ones, where you can enable
many of them with a wildcard, therefore it is not particularly useful
to have different ones per file