Add support for JSON-LD result sets

[LaurensRietveld]

For construct and describe queries allow the result format 'JSON-LD' to be set in the settings pane.

Apply syntax coloring to the obtained JSON-LD reply body (preferably JSON-LD-specific coloring, and otherwise generic JSON-coloring).

(copied from https://github.com/Triply-Dev/YASGUI.YASR-deprecated/issues/110)