Improve icons in the Input Map editor
Improve icons in the Input Map editor

- Add a disabled icon for built-in inputs with a tooltip explaining
  why they can't be removed. This also makes the Add button's horizontal
  position consistent between built-in and custom inputs.
- Fade out input event icons slightly to make them easier to distinguish
  from action icons.
- Remove unnecessary punctuation from mouse button and joypad event
  descriptions.

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