date 5.x-2.7

- #452420 Revert change of hyphen to dash in date display, dash is handled badly by token and elsewhere.
- #347080 Using 'first' and 'last' is more reliable than '+1 week' in strtotime().
- #369020 Fix bug when finding first or last Mon/Tue/Wed/Thu/Fri/Sat/Sun of month.
- #427830 Postgres can't handle \T.
- #417032 Fix typo that caused date fields using text widget not to have values saved.
- #418206 All date elements should be in datetime format when processing elements.
- #375864 Clean up date_limit_format() to handle more odd formats.
- #338253 Fixes to translation of timezone names.
- #409476 Make sure empty UNTIL date is not parsed into RRULE.