[Frontend] Inspector-related fixes

open #244
Fixing scroll issue in Inspector via flex layout;
Added new _archetypes.scss file for .l-flex* and .col styles;
moved .col and associated mixin out of _layout.scss
and into _archetypes;

platform/commonUI/general/res/templates/object-inspector.html

@@ -20,9 +20,9 @@
  at runtime from the About dialog for additional information.
 -->
 <span class="l-inspect" ng-controller="ObjectInspectorController as controller">
-    <div class="abs holder holder-inspector-elements">
-    <div class="pane-header">Inspection</div>
-    <ul>
+    <div class="abs holder holder-inspector-elements l-flex-col">
+    <div class="pane-header flex-elem">Inspection</div>
+    <ul class="flex-elem grows vscroll">
         <li>
             <em>Properties</em>
             <div class="inspector-properties"