GStreamer solution implemented and working. CMake bulding not quite there yet with .dll-files not finding to the bin folder and some code cleanup needed before potential merge with master

Added some allowed IP-addresses to the config-file in order to access the GUI remotely. Changed GUI host from localhost to local IP address. Also changed size of Spout window.

Add more informative error when a layer fails specification;  Add error message when trying to unzip a file that does not exist

Feature/sgct json

* Add some missing renderables
* Tiny refactor of documentation identifiers and log category keys

For consistency. This has bothered me for quite a while

Don't think it should be a breaking change, as the keys in any potential assets are obtained from the codegen/documentation parameters

And make property title formatting more consistent

closes #1822 

Feature/tileproviders

* "newPosition" is now considered to be the item's new position (index) in the list
* also update the documentation a little