Warn if keybinds are defined twice (closes #899)

Update Ghoul

data/assets/util/scene_helper.asset

@@ -1,18 +1,23 @@
-local bindKeys = function(t)
-    for i, k in ipairs(t) do
-        local bindFunction
+local bindKeys = function(t, ignoreWarning)
+    ignoreWarning = ignoreWarning or false
+    for _, k in ipairs(t) do
+        assert(k.Key, 'No key provided')
+        assert(k.Command, 'No command provided for key ' .. k.Key)
+
+        k.Name = k.Name or k.Key
+        k.GuiPath = k.GuiPath or ''
+
+        local currentKey = openspace.getKeyBinding(k.Key)
+        if (next(currentKey) ~= nil) and (not ignoreWarning) then
+
+            openspace.printWarning('New keybind for "' .. k.Key .. '" is added, but a previous keybind already existed. If you want to silence this warning, pass "true", to this call to bindKeys')
+        end
+
         if k.Local then
-            bindFunction = openspace.bindKeyLocal
+            openspace.bindKeyLocal(k.Key, k.Command, k.Documentation, k.Name, k.GuiPath)
         else
-            bindFunction = openspace.bindKey
+            openspace.bindKey(k.Key, k.Command, k.Documentation, k.Name, k.GuiPath)
         end
-        if k.Name == nil then
-            k.Name = k.Key
-        end
-        if k.GuiPath == nil then
-            k.GuiPath = ""
-        end
-        bindFunction(k.Key, k.Command, k.Documentation, k.Name, k.GuiPath)
     end
 end
 asset.export("bindKeys", bindKeys)
@@ -21,12 +26,8 @@ local unbindKeys = function(keys)
     -- We check against k and k.Key to provide compatability
     -- for both calls with the same table that goes to bindKeys
     -- as well as the return values from setDeltaTimeKeys
-    for i, k in ipairs(keys) do
-        if k.Key then
-            openspace.clearKey(k.Key)
-        else
-            openspace.clearKey(k)
-        end
+    for _, k in ipairs(keys) do
+        openspace.clearKey(k.Key or k)
     end
 end
 asset.export("unbindKeys", unbindKeys)