Location and timing

In #333 (closed) we renamed "Location and timing" to "Location".

The backend (genesys-pgr/genesys-server!182) now supports setting startDate and endDate properties in Location class and it provides the minimum and maximum start and end dates in the Dataset. Update the models accordingly.

UI updates

In the DatasetLocation edit form add two input fields:

• Start of evaluation
• End of evaluation

The placeholder value should be YYYYMMDD. The backend accepts strings in "MCPD format": 20180803 is 03 Aug 2018, while 199001-- is simply Jan 1990 and 1980---- is only 1980.

Update the dataset and location display components to include the start and end of evaluation periods.