[Device] Fix dlr_device_set_position implementation

dlr_device_set_position is incorrectly implemented.
now we use the REL_TIME unit for Time based Seeking
instead of ABS_TIME unit and the X_DLNA_REL_BYTE unit for
Byte Seeking instead of ABS_COUNT unit.

Partial fix for issue:

https://github.com/01org/dleyna-renderer/issues/115

Signed-off-by: Christophe Guiraud <christophe.guiraud@intel.com>
[Device] Fix DLR_INTERFACE_PROP_BYTE_POSITION retrieval

DLR_INTERFACE_PROP_BYTE_POSITION is now assigned with
the result of a call to upnp action X_DLNA_GetBytePositionInfo[RelByte]
instead of upnp action GetPositionInfo[RelCount].

Partial fix for issue:

https://github.com/01org/dleyna-renderer/issues/115

Signed-off-by: Christophe Guiraud <christophe.guiraud@intel.com>
[Device] Fix dlr_device_seek implementation

dlr_device_seek was incorrectly implemented.
Modify the current implemention to retrieve the current position with
the right method depending on the unit (time or byte) and add it to
the delta specified in Seek request, and then call
dlr_device_set_position().

so now we have:

- TIME SEEK OPERATIONS

Seek(offset)
 -> current_position = UPNP GetPositionInfo["RelTime"]
 -> UPNP Seek["REL_TIME", current_position +  offset]

SetPosition(position)
 -> UPNP Seek["REL_TIME", position]

- BYTE SEEK OPERATIONS

ByteSeek(offset)
 -> current_position = UPNP X_DLNA_GetBytePositionInfo["RelByte"]
 -> UPNP Seek["X_DLNA_REL_BYTE", current_position + offset]

SetBytePosition(position)
 -> UPNP Seek["X_DLNA_REL_BYTE", position]

Partial fix for issue:

https://github.com/01org/dleyna-renderer/issues/115

Signed-off-by: Christophe Guiraud <christophe.guiraud@intel.com>
[Device] Check X_DLNA_GetBytePositionInfo action availability

Introspection is used to check if the UPnP X_DLNA_GetBytePositionInfo
action is supported. If it is not supported we skip its call when we
retrieve all the properties.
X_DLNA_GetBytePositionInfo doesn't seem to be widely supported by
renderer devices.

Partial fix for issue:
https://github.com/01org/dleyna-renderer/issues/115

Signed-off-by: Christophe Guiraud <christophe.guiraud@intel.com>