Merge branch 'hotfix/#6655-#6649-allow-empty-form-element-value-options-in-form-element-renderer'

Close #6655
Close #6649
* hotfix for plural issue with wrong gettext loader
* new test for I18n/Translator/Loader/Gettext
fix for crashed GettextTest in PHP 5.3
#6765 #6762 - minor CS fix (spaces around parentheses)
#6765 #6762 - adding `@group` annotations for newly introduced tests
#6765 #6762 - minor cs fixes (one argument per line in multiline function calls, spacing)
Merge branch 'hotfix/#6762-#6765-fix-wrong-gettext-plural-translation' into develop

Close #6762
Close #6765
Forward port #6762
Forward port #6765