Bug 15395: Allow correct handling of plural translation

Bug 15395: Allow correct handling of plural translation

Locale::Maketext does not allow correct handling of plural translation
for languages that have more than one plural forms.
Locale::Messages does.

So Koha::I18N is now a wrapper around Locale::Messages, just like
Locale::TextDomain, and export the same symbols as Locale::TextDomain.
You can refer to documentation of Locale::TextDomain to know how to use
exported subroutines.

Example usage:
  __("Hi")
  __x("Hi {name}", name => 'Bob')
  __n("item", "items", $num_items)
  __nx("one item", "{count} items", $num_items, count => $num_items)
  __p("Bibliographic record", "item")

This patch also brings Koha::I18N power to Template::Toolkit templates
by adding a TT plugin.
This plugin can be used like this:

[%# USE the plugin and define some macros %]
[% PROCESS 'i18n.inc' %]

[%# tn is the equivalent of __n %]
[%# macro names can't start with underscore, t is for "translate" %]
[% tn('item', 'items', num_items) %]
Extraction of strings from templates is a bit complicated and use
Template::Parser and PPI. Template is compiled into Perl code and then
analyzed by PPI. It is slow, but should be correct even with complex
constructions.

Remove dependency to Locale::Maketext and Locale::Maketext::Lexicon
Add dependency to Locale::Messages and PPI

Test plan for translation in Perl code:
1. Open a .pl script or .pm module with your favorite text editor
2. Add 'use Koha::I18N;' in the beginning of file
3. Use one of the subroutines exported by Koha::I18N and be sure to have
   a way to visualize the result (pass result to the template for
   example, or simply warn and watch the log file)
4. cd misc/translator && ./translate update fr-FR # try other languages
5. Open misc/translator/po/fr-FR-messages.po and translate your
   string(s)
   You may need to change the "Plural-Forms" header. See
   https://localization-guide.readthedocs.org/en/latest/l10n/pluralforms.html
6. ./translate install fr-FR
7. Use your web browser to go to the page that should display the
   translation, change language and verify the translation is correct
8. prove t/Koha/I18N.t

Test plan for translation in templates:
1. Open a template file (.tt or .inc) with your favorite text editor
2. Add the PROCESS directive mentioned above in the beginning of file
3. Use one of the t* macros defined in i18n.inc. They are used like
   their "__" equivalent, with one difference: the 'x' variants take a
   hashref instead of a hash as last parameter
4. cd misc/translator && ./translate update fr-FR
5. Open misc/translator/po/fr-FR-messages.po and translate your
   string(s)
6. ./translate install fr-FR
7. Use your web browser to go to the page that should display the
   translation, change language and verify the translation is
   correct

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>