i18n service improved

Added sanitiser for l10n messages
Supported basic markdown for translations
Improved insertParams function
AppUsersManager i18n bugfix
Partially migrate modal views to msgid

Group create
Group edit
Group view
Confirm
Migrate remaining modal views to msgid
migrate remaining partials to msgid
migrate modules to msgid
escape html in msgstrs before markdown and param insertion

using encodeEntities(msgstr) earlier allows for a much simpler
parseMarkdownString() and we can always insert the messages as html
safely
some minor bugfixes
migrate pluralize directives to msgid
migrate german locale to msgid