bug 811762 - Port ESR download page to Bedrock

Fix for 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.

https://bugzilla.mozilla.org/show_bug.cgi?id=811762
Before this can be merged into the head repo, product_details must be updated to include a firefox_version "FIREFOX_ESR_QA". A patch is present in the bug page which adds such entry plus a 17.0.2esr build to all languages with 10.0.12esr.