Remove code to find Weston libdir

This is not necessary anymore because the Weston plugin is installed
under Hawaii Shell path since Weston can now load plugins with
absolute paths.
Make GreenIsland a required dependency

Always build the compositor because we want the QML compositor to be
ready for an early preview as soon as possible.
polkit-agent: Move PolicyKit agent out of the shell

Move the code to a separate process.
It doesn't build now and will be fixed later.

Issue: #146
systemd: Add PolicyKit agent unit

Issue: #146
Make PolicyKit requirement optional

With the PolicyKit agent being a separate process we can allow people
building this module without it.

Issue: #146
Move QtAccountsService check to the root CMakeLists.txt

A couple of components now require it (PolicyKit agent and the
indicators element) so this is a better place to put the check.
Install the indicators element only if QtAccountsService is available

It is using QtAccountsService QML API so we better check if it's
available before installing it.
polkitagent: Turn PolicyKitAgent into a singleton

We only have one instance of it anyway.

Issue: #146
polkitagent: Add main

Issue: #146
polkitagent: Cleanup

Issue: #146
polkitagent: Notify services manager

Notify systemd upon startup.

Issue: #146
lookandfeel: Clean authentication dialog

Make it work outside the shell.

Issue: #146
polkitagent: Load authentication dialog from package

Issue: #146
libhawaiishell: Fix look and feel definition

Directories and components had the same name.
components: Link components QML plugin to Wayland client library

This is needed to use Wayland protocols.