Adds thank-you page shown after submitting a reservation.

Each resource may have a custom text which is shown under the thank you note. Closes #138.

Squashed commit of the following:

commit a85d5784bc8665b4c0a151ee517327133a9167d8
Author: Denis Krienbühl <denis@href.ch>
Date:   Fri Jun 20 15:00:25 2014 +0200

    Updates German translation

commit 1ed427d3ea824098061056c29aa0347c49ad31df
Author: Denis Krienbühl <denis@href.ch>
Date:   Fri Jun 20 14:57:37 2014 +0200

    Adds tests for thank you page

commit 4a16559ca9a97d763806a4423dd7cc5781e2443f
Author: Denis Krienbühl <denis@href.ch>
Date:   Fri Jun 20 14:17:30 2014 +0200

    Adds working thank you texts

commit b02e458ec56d208b426165ce11e56fde64b4a266
Author: Denis Krienbühl <denis@href.ch>
Date:   Fri Jun 20 13:17:11 2014 +0200

    Adds an initial static thank you page. Proof of conceptish.