Refactor colors in internal commands

Originally this started as a "deduplicate a bunch of duplicated code in script commands" PR,
but as I was working on that, I discovered there's a lot more that needs to be done than
just deduplication.
Anything which needs a crewmate entity now calls `getcrewmanfromname(name)`, and anything which
just needs the crewmate's color calls `getcolorfromname(name)`. This was done to make sure that
everything works consistently and no copy/pasting is required. Next is the fallback; instead of
giving up and doing various things when it can't find a specific color, it now attempts to treat
the color name as an ID, and if it can't then it returns -1, where each individual command handles
that return value. This means we can keep around AEM -- a bug used in custom levels -- by not
doing anything with the return value if it's -1.

Also, for some reason, there were two `crewcolour` functions, so I stripped out the one in
entityclass and left (and modified) the one in the graphics class, since the graphics class also
has the `crewcolourreal` function.

desktop_version/src/Game.cpp

@@ -3630,7 +3630,7 @@ void Game::updatestate(void)
                 }
                 obj.entities[i].invis = false;
                 obj.entities[i].dir = 1;
-                obj.entities[i].colour = obj.crewcolour(lastsaved);
+                obj.entities[i].colour = graphics.crewcolour(lastsaved);
 
                 obj.entities[i].ay = -6;
                 obj.entities[i].ax = 6;