Adds randomize button in case of level with no thangs

app/styles/editor/level/thangs_tab.sass

@@ -210,6 +210,21 @@ $mobile: 1050px
     #canvas-wrapper
       width: 100%
       position: relative
+
+      #canvas-overlay
+        position: absolute
+        width: 100%
+        height: 100%
+        background: white
+        opacity: 0.5
+        text-align: center
+
+        #randomize-button
+          position: absolute
+          top: 45%
+          height: 40px
+
+
   
     // Below snatched from play/level.sass; should refactor?
   

app/templates/editor/level/thangs_tab.jade

@@ -23,6 +23,8 @@ button.navbar-toggle.toggle.btn-primary#thangs-palette-toggle(type="button", dat
 .world-container.thangs-column
   h3(data-i18n="editor.level_tab_thangs_conditions") Starting Conditions
   #canvas-wrapper
+    #canvas-overlay
+      button.btn.btn-primary(id="randomize-button", data-toggle="coco-modal", data-target="editor/level/modals/TerrainRandomizeModal", data-i18n="editor.randomize", title="Randomize Terrain") Randomize
     ul.dropdown-menu#contextmenu
       li#delete
         a(data-i18n="editor.delete") Delete

app/views/editor/level/thangs/ThangsTabView.coffee

@@ -116,6 +116,8 @@ module.exports = class ThangsTabView extends CocoView
     $(window).resize @onWindowResize
     @addThangsView = @insertSubView new AddThangsView world: @world, supermodel: @supermodel
     @buildInterface() # refactor to not have this trigger when this view re-renders?
+    if @thangsTreema.data.length 
+      @$el.find('#canvas-overlay').css('display', 'none')
 
   onFilterExtantThangs: (e) ->
     @$el.find('#extant-thangs-filter button.active').button('toggle')
@@ -233,6 +235,8 @@ module.exports = class ThangsTabView extends CocoView
       @addThang @addThangType, thang.pos, true
     @batchInsert()
     @selectAddThangType null
+    @$el.find('#canvas-overlay').css('display', 'none')
+
 
   # TODO: figure out a good way to have all Surface clicks and Treema clicks just proxy in one direction, so we can maintain only one way of handling selection and deletion
   onExtantThangSelected: (e) ->