Viewer enhancements and Viewer Dialog prototype (#2200)

* viewer dialog scaffold

* toolbar divider component

* simple error screen

* material module and tooltips

* show file name in the title

* improved settings, simple image viewer

* flex-based image viewer, minor fixes

* ability to switch between viewers

* single viewer for images

* remove MDL from the Viewer component

* remove hardcoded demo shell layout

remove harcoded assumptions on "header" and "main" elements

* rework text viewer, remove MDL dependency

* upgrade 'unknown format' view, remove MDL

* simplify media viewer layout

* simplify image viewer

* clean pdf viewer

* migrate pdf viewer styles to scss

* rewrite pdf viewer host styles in scss

* fix unit tests and cleanup layout

* file viewer service

* viewer dialog supports downloads if url provided

ng2-components/ng2-alfresco-viewer/src/components/notSupportedFormat.component.scss

@@ -0,0 +1,5 @@
+.adf-not-supported-format {
+    .mat-card {
+        max-width: 400px;
+    }
+}