Update Ubuntu install instructions

Removed need to install snapshot version for latest Ubuntu now that 1.28 is packaged.
just update the perldoc parts
Send keepalive messages if the rtsp server supports this feature
Use our own SSRC when sending packets on the control stream
Use our own SSRC when sending packets on the control stream
add comment to improve understanding
Merge branch 'master' of github.com:ZoneMinder/ZoneMinder
Merge pull request #561 from manupap1/rtsp_fix2

Use our own SSRC when sending packets on the RTP control stream
Merge pull request #560 from manupap1/rtsp_fix

Send keepalive messages if the rtsp server supports this feature
Merge pull request #550 from SteveGilvarry/patch-1

Update Ubuntu install instructions
Update skin.js

Fix issue caused by a previous merge