qt: qml: refactor player control handling

* PlayerControlbarModel class is repurposed
and renamed to "player_controlbar_model.cpp/hpp".
PlayerControlbarModel is now a supermodel that
instantiates and handles three ControlListModel
for its 'left', 'center', and 'right' properties.
ControlListModel is the stripped down version of
the old PlayerControlbarModel.

* ControlbarProfileModel is created during
MainInterface initialization. ControlbarProfileModel
creates and handles toolbar/controlbar profiles
that act as a wrapper of PlayerControlbarModel
instances. Saving and loading from settings
happens in ControlbarProfileModel.

* Default control layout is now defined in
ControlbarProfile class. ControlbarProfile
injects the default configuration
during construction.

* Default profiles are now defined in
ControlbarProfileModel class.
ControlbarProfileModel class automatically
matches defaults based on player identifiers.

Signed-off-by: Pierre Lamot <pierre@videolabs.io>