Improved loading indicators. Added % loaded to viewports and thumbnails

Packages/viewerbase/components/studyBrowser/imageThumbnail/imageThumbnail.styl

@@ -2,4 +2,22 @@
   width: 90px
   height: 90px
   background-color: black
-  margin: 0 auto
+  margin: 0 auto
+  position: relative
+  
+.thumbnailLoadingIndicator
+  display: none
+  pointer-events: none
+  color: #f8a13f
+  height: 20px
+  width: 100%
+  top: 0
+  left: 0
+  right: 0
+  bottom: 0
+  margin: auto
+  position: absolute
+  
+  p
+    text-align: center
+    font-size: 10pt