Added automated test for UTC date ticks and labels.

Added automated test for UTC date ticks and labels.

The date tick tests are broken in the ticker automatic test suite
because they assume EST timezone. In addition, the suite is disabled.
Fix the  automatic test suite for the case UTC ticks and labels:

  * `auto_tests/tests/date_ticker.js`:
    Test the generation of ticks and labels at nice time positions
    according to UTC as set by option `labelsDateUTC`.
    Include the date axis tests from `auto-tests/tests/tickers.js-disabled`
    with the required changes of timestamps and with initial ticks
    out of range removed.