Cleanup tools & main rendering

Tools were a mess, spread all over the code with hundreds of `else-if`
statements. Instead of magic numbers denoting tools, an enum has been
created, and logic has been extracted into simple switch/cases, shared
logic being deduplicated.

The base of a state system for the editor has been created as well,
laying a good path for further organization improvements. Because of
this, the entire editor no longer gets drawn underneath the menus,
except for a few pieces which I haven't extracted yet. Either way,
this should be good for performance, if that was a concern.

desktop_version/src/Game.h

@@ -412,7 +412,6 @@ public:
     int quick_trinkets;
     std::string quick_currentarea;
 
-    int mx, my;
     int screenshake, flashlight;
     bool advancetext, pausescript;