Bitmapper: Fix closure warnings, fix release build.

Bitmapper release build currently spews console errors.

This eliminates all the Closure warnings, and adds the magical
incantations to allow the existing Polymer elements to behave in a
release build.

Keycode handling of digits 1-5 is removed, since it is broken: typing
into the resize textboxes would cause random tools to get selected.
Worse, under release, these tools are actually undefined when accessed
in this manner.

To help future fixes:
 - Makes the whitespace in the release build pretty-printed.
 - Skips linting exerns.js

Some externs were out of date and are removed.

To fix Polymer in release, access to fooChanged/fooValue need to be via
string or externs. externs are added for Polymer elements hanging off
`$`. For things hanging off HTMLElement, externs are not really
sustainable, so these are also indexed via string. TODO: These need a
better hack.

BUG=https://github.com/jackhou-chromium/bitmapper/issues/14
R=hbeder@google.com

Review URL: https://codereview.appspot.com/191240043