Add search.js, rebase search system on top

The high level goal is to separate the concern of searching for
things with display of those things; for example in newer mockups,
applications are displayed exactly the same as they look in the
AppWell.

Another goal was optimizing for speed; for example,
application search was pushed mostly down into C, and we avoid
lowercasing and normalizing every item over and over.

https://bugzilla.gnome.org/show_bug.cgi?id=603523

js/ui/overview.js

@@ -184,6 +184,7 @@ Overview.prototype = {
         this._dash.actor.set_size(displayGridColumnWidth, contentHeight);
         this._dash.searchArea.height = this._workspacesY - contentY;
         this._dash.sectionArea.height = this._workspacesHeight;
+        this._dash.searchResults.actor.height = this._workspacesHeight;
 
         // place the 'Add Workspace' button in the bottom row of the grid
         addRemoveButtonSize = Math.floor(displayGridRowHeight * 3/5);