Bug 18629 - Translatability: Fix problems with web installer 17.05

Bug 18629 - Translatability: Fix problems with web installer 17.05

The new web installer for 17.05 has a great new design - but it has a lot of
translatability issues. Some strings are not picked for translations,
some expose the content of tt directives, and others are splitted by
html tags, resulting in small text fragments that are not easy to translate.

This patch weeds out such translation problems for step1.tt, step2.tt and
step3.tt

To test:
- Apply patch (on top of Bug 18665 because of html tags inside of
  tt directives in step2.tt)
- Prepare a fresh install (drop database, create database)
- Walk through the installation process and verify that it works as before
- Verify that string changes (in English) make sense
- Create a translation( cd misc/translator, then perl translate create aa-AA)
  then: vim po/aa-AA-staff-prog.po and search for: /installer\/step
  Verify that strings for step1.tt, step2.tt, step3.tt are not fragmented,
  do not contain [%%, and are easily translatable (make sense without having
  to search in source files for context).

(Amended to remove some superfluous chomps 2017-06-27 mv)

Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>