Added method to DateUtil to calculate days in between two dates

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.1.0 CE GA1, 6.1.10 EE GA1, 6.2.0 CE M2
• Fix Version/s: 6.1.20 EE GA2, --Sprint 11/12, 6.2.0 CE M2
• Component/s: Legacy Components, Legacy Components > API
• Labels: None
• Branch Version/s:
  6.1.x
• Backported to Branch:
  Committed
• Git Pull Request: https://github.com/wesleygong/liferay-portal/pull/8

New method to calculate the days in between two dates.

public static int getDaysBetween(Date date1, Date date2)