Add setactivitycolour(colour) and setactivitytext() commands

These commands will change the colour and text of the next
activity zone that gets spawned. `setactivitycolour` takes all
textbox colors, and `setactivitytext` will take the text on
the next line. These commands were designed this way
to avoid breaking forwards compatibility.

desktop_version/src/Entity.h

@@ -193,6 +193,8 @@ public:
     bool customwarpmode, customwarpmodevon, customwarpmodehon;
     std::string customscript;
     bool customcrewmoods[Game::numcrew];
+    std::string customactivitycolour;
+    std::string customactivitytext;
 };
 
 #ifndef OBJ_DEFINITION