bug 811762 - Port ESR download page to Bedrock

Added new ESR languages page, which can display both current ESR and QA ESR builds. To work, it requires product_details to export a new entry 'FIREFOX_ESR_QA' in firefox_versions, even if it is just an empty string.

Fixed download_buttons.py problem with FIREFOX_ESR_QA. Added new version to test data.