Fixes #459 - adds google translate env variable

Adds an environment variable for the Google Translate customization
code provided by the Google Translator Widget Wizard.
Simplifies Google Translate Widget

Simplifies Google Translate Widget to use Dropdown only display mode
and sets translation to all languages by default instead of leaving out
Latin, Esperanto and Welsh. This avoids listing out the included
languages.
Merge pull request #540 from codeforamerica/459-google-translate-customization

459 google translate customization