Added an example streaming source

This new source works with the streaming particles plugin as an example of how
to write a source to generate streaming blocks.

Change-Id: I99fab1a82e476fca0b7b857b25b1e0bc1e3d58f2
Removed GUI resouce xml files from other plugins

Change-Id: I126cb600d1519025cf5fd5b1c746ba22ee213f5e
Sources with FileName attribute now appear in menu

This change breaks backwards compatibility in that file readers must now
use the hints mechanism to tell the ReaderFactory that they are readers
to avoid showing up in the sources menu.  But this is preferable to
sources that have a FileName but are not really readers being hidden.

Change-Id: I008a86270ab0028b426093472f0ee5c96e50ceeb
Updated CMake to ignore plugin GUI xml files

Change-Id: I8ede532335a16304d96172993ce41c30350e0f0c
Updated Major API Changes document

Plugin GUI xml files are no more and this is a major API change.

Change-Id: I99e89ac8fbb93f847637751ea07e79c87d356f59
Merge topic 'simple-streaming-source' into next

0dd3fb09 Updated Major API Changes document
6b4d8cfd Updated CMake to ignore plugin GUI xml files
57198728 Sources with FileName attribute now appear in menu
4c2ce814 Removed GUI resouce xml files from other plugins
5cff9763 Added an example streaming source