Handle batch request templates when generating subject

The preview view calls this function and we need to extend it to handle
batch requests.
Update link to point to change request form
Add sections on the Write API and anonymous users.

Contributes to https://github.com/mysociety/alaveteli/issues/1286
Add google's machine translation of English text.
Remove banner requesting help.

Closes https://github.com/mysociety/alaveteli/issues/1312
Merge branch 'remove-welsh-help-banner' into develop
Merge branch 'master' into develop

Conflicts:
    lib/views/general/_popup_banner.html.erb
Merge branch '1286-explain-anonymous-requests' into develop
Merge branch '1176-automate-authority-contacts' into develop
Merge branch 'feature/batch-requests' into develop
Merge branch 'master' into develop
Merge branch 'develop'