Added busy state event to pipeline js, also fired addSource when file loaded.

The new busy status event is fired with an argument of true before each rpc
call, and then fired again with false when the rpc call finishes, whether
the call failed or finished successfully.  This will allow widgets to
know about the busy state of the pipeline and respond accordingly.  Also
added code to fire a pipeline addSource event when a data file has finished
loading.

Change-Id: I3fb1e7fee84e20bd3f5ad443b5a5d8996917fd24
Added new protocols to dynamically load plugins and filters.

Added two new paraviewweb protocols.  One allows to specify a list
of plugins to be loaded upon startup of the web application.  The
other allows to specify a list of filters in a json text file which
will be available in the web application.  This is an improvement
on the static filter list previously provided by the pipeline
manager protocol.  The web visualizer application has been updated
to give examples of how these two protocols are used.

Change-Id: I0d2f556347a777a04c82c7b04613ee6c8a3d2f9a
Update documentation to reflect recent pvweb changes.

Change-Id: I28b5cbf3a42584732f4894586329bf1cd47be7ac
Added documentation of startup protocols as a new group within Server.

Change-Id: I6304b6439dc783cf69d0caa5deda74492d787685
Merge topic 'pvweb-enhancements-events-protocols-docs' into next

b931684 Added documentation of startup protocols as a new group within Server.
a94dcff Update documentation to reflect recent pvweb changes.
3853adb Added new protocols to dynamically load plugins and filters.
5e497a9 Added busy state event to pipeline js, also fired addSource when file loaded.