add lightmediascannerd and lightmediascannerctl

add lightmediascannerd and lightmediascannerctl

The daemon and control client are provided as a way to make usage of
lightmediascanner easier in a platform. It will scan directories based
on the startup configuration of categories, their parsers and
directories.

One can request a write lock, avoiding the server to scan and also
report to others that they should not write to DB.

Scanning status, Write Lock and global Update ID are provided as
properties.

The scan method will take a dict of categories and their respective
scan paths. This allows to reduce the scan scope to just few
categories and paths. The categories must exist previously and paths
must be inside the previously known categories directories, this
avoids people doing mistakes. If a category is provided as an empty
list, all directories will be used. If there are no categories
provided, then all categories with all directories will be used.