keyboard: Define settings from QML

Don't use a C++ object to manage settings, just use the new QML
component.
Install preflets as packages

Issue: #28
Rename PolkitQt-1 to PolkitQt5-1
Add metadata desktop files and convert them to JSON

Those files are converted to JSON metadata with a script.
Move desktop entries sources along with metadatas

These are sources files just like metadata in desktop format and they
need to be together.
Check for HF1HawaiiShell

It's needed to load preference packages.
app: Load preflets from packages

Preflets are now shipped as packages.
declarative-background: Install qmldir

Install qmldir file so that the plugin is actually usable.
background: Rename identifier to internalName

Follow Hawaii Shell changes.