Bug 819557 - Enable Get involved page for Turkish (tr)

Usual stuff:
* add localized banner + css rule
* add email address and locale code to 15 years template

Both pages are still not activated on stage/prod, since I'd like to
enable them once this PR is available on production (if I activate them
now the page will show up with the old template).
Merge pull request #1352 from flodolo/bug819557_tr_getinvolved

Bug 819557 - Enable Get involved page for Turkish (tr)