Update webL10n to latest version + features

Base version of l10n:
- https://github.com/fabi1cazenave/webL10n/tree/b18c753c6f
4 extra commits (expected to be accepted):
- https://github.com/fabi1cazenave/webL10n/pull/38

New features compared to mozL10n:
- Support for getting translated attributes in get()

The previous version of mozL10n was based on:
- https://github.com/fabi1cazenave/webL10n/commits/0c06867a75
- diff: http://pastebin.mozilla.org/3061694

To make it easier to update webL10n in the future, I will apply
the PDF.js-specific changes in a separate commit.
webL10n: Apply PDF.js-specific changes

Based on http://pastebin.mozilla.org/3061694

1. Remove "debug helpers" and use console.log/console.warn directly (top).
2. Remove page load initialization (middle).
3. Remove window._ alias (bottom)

The original diff contained an extra entry
"Adds fallback argument to the getL10nData;",
but this was already implemented in the rebased webL10n, so it's no
longer PDF.js-specific.
Merge pull request #3696 from Rob--W/webL10n-tot

Update webL10n to latest version (september 2013) (+support for attributes in mozL10n.get)