[Tizen] Move MediaServer dbus objects to worker thread

This patch adds new worker thread with g_main_loop for async
dbus call processing.
Add OWNERS
Merge pull request #296 from halton/owner

Add OWNERS
Bump version to 0.54
Merge pull request #291 from alexshalamov/add_worker_thread_to_mediaserver

[Tizen] Move MediaServer dbus objects to worker thread
[Tizen] Add support for missing virtual roots

This patch adds support for missing virtual roots:
wgt-package, wgt-private, wgt-private-tmp and ringtones.
Merge pull request #290 from alexshalamov/implement_widget_storage_support

[Tizen] Add support for missing virtual roots
[TEMP] Fix coding style check error

This commit can be reverted after cpplint.py updated with
CL https://codereview.chromium.org/269013009/
Merge pull request #299 from halton/style

[TEMP] Fix coding style check error
[Content] TCT crash and passrate fixes

Implement scanFile method which is heavily used by the TCT web api test suite.

Fix a crash for filter with invalid parameters (no bug yet).

Rename uri to path conversion methods more aligned with chromium.