Implement camera orbiting shortcuts.
Implement camera orbiting shortcuts.

Fixes godotengine/godot-proposals#2051.
Relates to godotengine/godot-proposals#1215.

Implements shortucts for adjusting the camera rotation in 15-degree
increments, similar to Blender.

I did not add corresponding menu entries for these, as I didn't feel
like they would be too useful from a menu, and didn't want to make the
menu too long.

pkowal1982/godot,godotengine/godot,Faless/godot,firefly2442/godot,guilhermefelipecgs/godot,vkbsb/godot,BastiaanOlij/godot,ZuBsPaCe/godot,godotengine/godot,pkowal1982/godot,Shockblast/godot,vkbsb/godot,vkbsb/godot,vnen/godot,akien-mga/godot,Valentactive/godot,ZuBsPaCe/godot,Shockblast/godot,vnen/godot,vnen/godot,Valentactive/godot,josempans/godot,BastiaanOlij/godot,josempans/godot,Shockblast/godot,guilhermefelipecgs/godot,pkowal1982/godot,Valentactive/godot,Zylann/godot,Shockblast/godot,pkowal1982/godot,josempans/godot,firefly2442/godot,guilhermefelipecgs/godot,sanikoyes/godot,guilhermefelipecgs/godot,BastiaanOlij/godot,vnen/godot,vkbsb/godot,vkbsb/godot,vnen/godot,sanikoyes/godot,sanikoyes/godot,BastiaanOlij/godot,firefly2442/godot,guilhermefelipecgs/godot,sanikoyes/godot,godotengine/godot,Faless/godot,ZuBsPaCe/godot,godotengine/godot,guilhermefelipecgs/godot,akien-mga/godot,Zylann/godot,godotengine/godot,pkowal1982/godot,Zylann/godot,josempans/godot,josempans/godot,guilhermefelipecgs/godot,Zylann/godot,josempans/godot,Shockblast/godot,Faless/godot,akien-mga/godot,ZuBsPaCe/godot,pkowal1982/godot,vkbsb/godot,firefly2442/godot,Valentactive/godot,Zylann/godot,Faless/godot,Valentactive/godot,akien-mga/godot,Valentactive/godot,sanikoyes/godot,pkowal1982/godot,Faless/godot,akien-mga/godot,Valentactive/godot,Shockblast/godot,akien-mga/godot,ZuBsPaCe/godot,pkowal1982/godot,vnen/godot,Zylann/godot,Shockblast/godot,Zylann/godot,Zylann/godot,godotengine/godot,akien-mga/godot,Valentactive/godot,Shockblast/godot,vnen/godot,guilhermefelipecgs/godot,vnen/godot,godotengine/godot,ZuBsPaCe/godot,firefly2442/godot,Faless/godot,BastiaanOlij/godot,sanikoyes/godot,vkbsb/godot,firefly2442/godot,BastiaanOlij/godot,firefly2442/godot,josempans/godot,Faless/godot,ZuBsPaCe/godot,BastiaanOlij/godot,akien-mga/godot,vkbsb/godot,Faless/godot,sanikoyes/godot,josempans/godot,godotengine/godot,firefly2442/godot,sanikoyes/godot,ZuBsPaCe/godot,BastiaanOlij/godot