Bug 18693: Translatability: Get rid of exposing a [%% FOREACH loop in translation...

Bug 18693: Translatability: Get rid of exposing a [%% FOREACH loop in translation for branch-selector.inc

The file branch-selector.inc exposes the following line to translation
(due to newlines insied a tt directive):
%s %s [%% FOREACH branch IN branches; IF branch.selected; selectall = 0; END; END %%]

Additionally, export.tt exposes the following line to translation:
[%% INCLUDE 'branch-selector.inc' branches = libraries %%]

To test:
- Apply patch
- In Staff client, go to Home > Tools > Export data
- Verify that library selection behaves as before
- Bonus test: Create a "language" aa-AA (perl translate create aa-AA
  from folder misc/translator, verify that lines mentioned above do
  no longer appear in aa-AA-staff-prog.po
- Run QA tools (newest version with test for newlines in tt directives)

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>