Fix bug where temporal coverage chart failed when there was no
beginDates in the index. See bug #6585. 

The Stats model will now use the earliest endDate as the firstBeginDate
if no beginDates are found. If not beignDates or endDates are found, a
blank chart is drawn.
Reset index values
Merge changes to AppModel
Merge branch 'master' of
https://code.nceas.ucsb.edu/git/nceas-staff/datadepot.git

Conflicts:
	metacatui/src/main/webapp/index.html