Add Video socket server.
Now can send image byte.
A demo video chat!!!!!!!
Update ImgUtil.java

Add decoder and encoder.
Video Socket Server
Auth implements VideoEventHandler
Use delegate to deal with all events.
Multi client support !!!!!
A better VideoClient class implemented.
Merge remote-tracking branch 'origin/VideoSS' into invigilator
AuthView use single slot.
add terminateButton and modify css.
Merge remote-tracking branch 'origin/invigilator' into VideoSS
separate Slot class
Merge VideoSS