Fix icons on WebOS

WebOS 4 apparently has a ligature bug that prevents icons with an underscore from working as intended.
This replaces them with either the corresponding CSS class or unicode escape code, depending on context.
Refactoring is needed in order to be able to use CSS classes everywhere, so in the interest of time, this does the best available currently.

Fixes #678

src/components/imageoptionseditor/imageoptionseditor.template.html

@@ -1,5 +1,5 @@
 <div class="formDialogHeader">
-    <button type="button" is="paper-icon-button-light" class="btnCancel autoSize" tabindex="-1"><i class="material-icons">arrow_back</i></button>
+    <button type="button" is="paper-icon-button-light" class="btnCancel autoSize" tabindex="-1"><i class="material-icons arrow_back"></i></button>
     <h3 class="formDialogHeaderTitle">
         ${HeaderImageOptions}
     </h3>