Fixed browser portibility issue.

Some browsers (such as Firefox) would display NaN for timestamp values.
This includes the values for First Activity, Last Activity, Active Period,
and Shift Duration. This was caused by one of JavaScript's Date constructrs,
which would parse timestamps of the format MM/DD/YYYY hh:mm:ss.fff tt
incorrectly. As a solution, I added a file to the project containing
custom Date methods called datetime.js. I then use a custom date parsing
method from datetime.js to construct the Date objects when parsing the log
files.

Additional Notes:

 - Added datetime.js to the script src files listed in freepoint/public
  /header.php and views/getfreepoint/analytics.php