Clean up i18n handling for the behavior tab.

As part of the ADT, we can set the i18n-content property on the HTML
elements to automatically load localized text.  We don't need to call
chrome.i18n.getMessage manually.
Add a few more i18n string cleanups.
Merge pull request #64 from mvrable/i18n

Clean up i18n handling for the behavior overlay.
playing with padding
Merge pull request #65 from adrifelt/fixcss

Modify the padding to look more like the mock
merging
.