add "anywhere" keybinding guard

docs/changelog.txt

@@ -70,6 +70,7 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 - `spectate`: improved documentation of features and functionality
 
 ## API
+- ``Gui::anywhere_hotkey``: for plugin commands bound to keybindings that can be invoked on any screen
 - ``Lua::PushInterfaceKeys()``: transforms viewscreen ``feed()`` keys into something that can be interpreted by lua-based widgets
 - ``Lua::Push()``: now handles maps with otherwise supported keys and values
 - Constructions module: added ``insert()`` to insert constructions into the game's sorted list.

library/include/PluginManager.h

@@ -301,6 +301,7 @@ namespace DFHack
     {
         // Predefined hotkey guards
         DFHACK_EXPORT bool default_hotkey(df::viewscreen *);
+        DFHACK_EXPORT bool anywhere_hotkey(df::viewscreen *);
         DFHACK_EXPORT bool dwarfmode_hotkey(df::viewscreen *);
         DFHACK_EXPORT bool cursor_hotkey(df::viewscreen *);
     }

library/modules/Gui.cpp

@@ -630,6 +630,10 @@ bool Gui::default_hotkey(df::viewscreen *top)
     return false;
 }
 
+bool Gui::anywhere_hotkey(df::viewscreen *) {
+    return true;
+}
+
 bool Gui::dwarfmode_hotkey(df::viewscreen *top)
 {
     // Require the main dwarf mode screen