Fix Chrome M34 styling

@devoncarew @dinhviethoa

This addresses the recent breakage of the UI in Chrome 34. The root cause is that applyAuthorStyle for custom elements has been phased out.

The PR mostly consists of the following:
 1. Importing Bootjack CSS into every widget via a shared /widgets/common/spark_widgets.css (which is also useful for easier controlling of other styling for all widgets at once).
 2. Lifting editorView, fileTreeView and file-item-context-menu with their respective styles from spark_polymer_ui.* to spark_polymer.*, so that Ace global styles and treeview styles (in particular set programmatically in files_controller.dart and such) can reach their respective elements without having to pierce through shadowDOM boundary.
 3. Removing the obsoleted spark.html and .css.
 4. Fixing and improving the styling of spark-suggest-box (which was inadvertently inherited from styling set for dialogs in spark_polymer_ui.css).
 5. Adding `noPadding` attribute to spark-button to work around the no-longer-working external setting of the padding from spark-menu-button.
 6. Other minor cleanups.

The two remaining problems are:
 1. The glyphs in the Run button and plus/minus buttons in the Settings dialog render incorrectly (something related to font-awesome styles).
 2. The text clearing X in spark-suggest-box doesn't show when typing.