Allow start/end year in date-picker to be set using w2ui.settings

Date-picker has hard-coded start and end years (1950 and 2020, respectively). This patch allows one to set those parameters through w2ui.settings, namely

  w2utils.settings['dateStartYear'] = 1800;
  w2utils.settings['dateEndYear'] = 2014;

thus, not limiting the range of possible dates in the date-picker widget