Added UT1 conversions

Added UT1 conversions using deltaT file from USNO which gives the difference between UT1 and TT. (deltaT = TT-UT1).
Created date formatter that support time systems.

Added AKDateFormatter which supports time systems such as UTC , UT1, TAI, or TT, but not time zones.
Bugfix in date formatting

Bugfix: Strings with dates (with time systems) were not correctly parsed because the time system was not recognised and used.
Added methods in NSDate category to create a date from a string.
Removed logging.
Merge branch 'refs/heads/time-functions' into develop