Do not check if loading plugins succeeded

Now some plugin on Linux can be loaded by us and some by gstreamer - so
we can not fail so early.

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Move initializing gstreamer to GstWrapper class

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Rename VideoPlayerBackend_gst file and class to GstVideoPlayerBackend

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Do not pretend we can compile without GStreamer

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Move GStreamer code to separate directory

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Made GstVideoPlayerBackend inherit from VideoPlayerBackend

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Moved interface of video player to VideoPlayerBackend

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Use Factory pattern for creating VideoPlayerBackend instances

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Field rename

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Use interfaces for videos

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Rename VideoPlayerBackendFactory to VideoPlayerFactory

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Clean unused includes

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>