WebmWriter: set segment-duration to 0 initially; this allows chrome to play unfinished files

Adds a method that allows sending application data through DTLS. Enables handling of received application data when DTLS-SRTP is enabled.

Adds a registerUser() method to SrtpControl. Needed for allowing multiple MediaStream-s to share an SrtpControl.

Throws an exception if deleting or renaming a file fails.

Correctly load jitsi-defaults.properties when running under WebStart

Demotes the logging of the statistics about the sent and received RTCP SR/RR reports because they are too frequent.

the duration was set to 44 ms before (because ebml->last_pts_ms is initialized to -1; frame_time = 45 is added)