[BUGFIX] Changes flattr to "auto-submit"

Builds url with all needed data and creates the
flattr "thing" on the first click and donation.

Change-Id: Ie60155d44858de43cb86f3a590def19f70c064c9
Resolves: #51721
Reviewed-on: http://review.typo3.org/31325
Reviewed-by: Tomas Norre Mikkelsen <tomasnorre@gmail.com>
Tested-by: Tomas Norre Mikkelsen <tomasnorre@gmail.com>