Add depthsense plugin and depthsense2src element

Submitted by Miguel Casas-Sanchez @miguelecasassanchez

Link to original bug (#733222)

Description

DepthSense is the name of the SDK used by Time-Of-Flight cameras based on SoftKinetic chip, f.i. DS325 [1] or Creative Senz3d [2]. This bug tracks the landing of a plugin and element to capture the 3D information, streaming 16-bit depth maps (sent as GRAY16_LE).

[1] http://www.softkinetic.com/products/depthsensecameras.aspx
[2] http://us.creative.com/p/web-cameras/creative-senz3d