allow timezone translations to be used in more than 1 page (i18n)

firstboot.i18n.sh: add /www/time.js to gargoyle_header_footer pages required (holds the timeStr object needed when the Language-LG/time.js page is loaded) + the Language-LG/time.js for timezone definitions.

common.js: now hold the timezone definitions; more than 1 page uses timezones (firstboot & time), so this saves carrying the object thru to the common.js parseTimezones function

Note: ordinary/localized firstboot.sh doesn't require the added /www/time.js page because localized timezone translations are carried within the /www/data/timezones.txt document