Started to update for Polymer 0.5.0.

So much broken... I suspect that dropdown menus can't be in shadow DOM
for the <loot-dropdown-menu>, and <loot-dialog> doesn't seem to work
either for some reason.
Fixed <loot-dropdown-menu>.

I think. It's not been tested thoroughly, as little else works.
Fixed <loot-dialog>.

The issues seem to have been due to the layered attribute being true by
default in Polymer 0.5.0. The layering complicates matters (it moves
dialogs into shadow DOM), and I don't think I need it, so it's been
disabled. I also removed the open property, as it conflicts with an
existing function name.
Fixed <loot-message-dialog>.

It was missing a dependency, and being populated too late. Also changed
an ID to a class to avoid possible conflict.
Fixed translation script for HTML imports.
More misc fixes.
Some attempts at speeding things up.

Adding plugin cards and list items is **incredibly** slow, and it wasn't
like this in Polymer 0.4.2. I'm not sure if I'm not doing something
right...
Updated for Polymer 0.5.1.

Which removed the label and icon attributes from paper-item elements.
Fixed editor toolbars not being initialised correctly.
Fixed menu icon spacing.
Removed plugin card menu hack.
Implemented scrollable tabs in plugin editor.
Implemented animated tab page changes.

The tab pages in the editor are zero-height though, I couldn't figure
out how to solve that, so I'll just go back to it later. The Polymer
elements are in, and that's what matters at this stage.
Added header overlay back in.

For disabling the toolbar use during editing.
Added toasts for feedback, removed dead function.
The last selected menu item shouldn't stand out.
Removed some unnecessary CSS overrides.

There's an attribute for that.
Implemented narrow mode drawer button.

However, the z-index values of the cards make them appear on top.
Fixed progress bar layout change.

Happened when updating to Polymer 0.5.
Fixed search crash.