Update currently available demos to 0.2.1 and test their compose on x86 and Jetson

[bwsw]

Update demos, readme, and compose files to use 0.2.1 after it is available.

Change source adapters for

• opencv_cuda_bg_remover_mog2
• nvidia_car_classification
• peoplenet_detector (blur from artist)
• line_crossing (RENAME TO: traffic_meter)

From RTSP to Video Loop Adapter (#136).

Modify sink adapters in compose to use embedded MediaMTX(#151) and remove separate MediaMTX from the compose.

Additionally:

• Address Encode ZMQ socket type and source information into socket URL #128 in all demos to decrease the number of environment variables used;
• Add compose build where necessary to avoid -samples image;
• Move *.webp images to demo directories from the common.
• Test on x86
• Test on Jetson