webui: Datetime parsing and formatting
    
    this patch implements:
    - output_formatter in field. It should be used in par with formatter. Formatter serves for datasource->widget conversion, output_formatter for widget->datasource format conversion.
    - datetime module which parses/format strings in subset of ISO 8601 and LDAP generalized time format to Date.
    - utc formatter replaced with new datetime formatter
    - datetime_validator introduced
    - new datetime field, extension of text field, which by default uses datetime formatter and validator
    
    Dojo was regenerated to include dojo/string module
    
    https://fedorahosted.org/freeipa/ticket/4194
    
    Reviewed-By: Adam Misnyovszki <amisnyov@redhat.com>