Move menu etc. back to spark_polymer_ui

Problems:
1) File filter control doesn't expand to full width on focus
2) "No matching files" is always displayed
3) The editor view has `height=0`. Changing that to `height=600px` shows the view.
Merge remote-tracking branch 'upstream/master' into move-menu-back-to-spark_polymer_ui

Conflicts:
	ide/app/spark_polymer.html
2 tiny fixes/cleanups
Merge remote-tracking branch 'upstream/master' into move-menu-back-to-spark_polymer_ui
Fix: #editorView was invisible
Fix: "No matching files" was always visible
Fix introduced bug: file tree view was too tall and would cause the UI jump up sometimes
Restore + rework: file filter expands to right, run and menu buttons hide
No-op refactoring
Clearer naming + fix "No matching files" showing up after clearing file filter
Renamings
Do not defocus file filter on ESC
Hide Run/menu buttons only when text is entered into file filter, not when it just gets focused
Merge remote-tracking branch 'upstream/master' into move-menu-back-to-spark_polymer_ui
Merge remote-tracking branch 'upstream/master' into move-menu-back-to-spark_polymer_ui

Conflicts:
	ide/app/spark_polymer.css
	ide/app/spark_polymer.dart
	ide/app/spark_polymer.html
Merge remote-tracking branch 'upstream/master' into move-menu-back-to-spark_polymer_ui

Conflicts:
	ide/app/spark_polymer_ui.dart
Fix splitter draggable reagon width being off-by-1 (too narrow) for 1px-wide splitter
Revert "Fix splitter draggable reagon width being off-by-1 (too narrow) for 1px-wide splitter"

This reverts commit 69885a14e743f0f778f95d98b68d702fd1649967.
Merge remote-tracking branch 'upstream/master' into move-menu-back-to-spark_polymer_ui
Restore event handler attachment for spark-menu-button->activate (somehow got lost)