New plural unit decision functions

Removed singular units from zero-units and added new unit functions with custom string support for multilingual support.

Example usage in HTML:
English:
<timer>{{ minutes }} {{ minuteUnit('minute','minutes') }} {{ seconds }} {{ secondUnit('second','seconds') }}</timer>
Estonian:
<timer>{{ minutes }} {{ minuteUnit('minut','minutit') }} {{ seconds }} {{ secondUnit('sekund','sekundit') }}</timer>