All values now gets correct max and min, added EnvironmentalCategory model & category field to EnvironmentalVariable

Previously, 'all values' actually didn't get all of the environmental values, and therefore even though the results were correct, the numbers displayed in environmentaData[0] and environmentalData[1] were incorrect.

Switched over to using an api_view to get the min and max values.

Also, added the error message to the top set of buttons too on the search page.

Added fields for environmental category #79 and populated with categories in latest EcologicalDBASE file.  Environmental search now asks users to choose a category.