Adds the range of years to the CSVs that are generated for any endpoints with start and end years

[BobTorgerson]

This PR adds the date range selected from any endpoint that has a start year & end year and puts it into both the metadata and the file name of the CSV files. This works for all of the Degree Day

Examples:

Temperature

• http://localhost:5000/temperature/65.0628/-146.1627/1940/2060?format=csv

Temperature in January

• http://localhost:5000/temperature/jan/65.0628/-146.1627/1940/1970?format=csv

Precipitation

• http://localhost:5000/precipitation/65.0628/-146.1627/1980/2080?format=csv

Degree Days

• http://localhost:5000/degree_days/freezing_index/65.0628/-146.1627/1990/2080?format=csv
• http://localhost:5000/degree_days/heating/65.0628/-146.1627/1970/2050?format=csv

Wet Days per Year

• http://localhost:5000/wet_days_per_year/projected/point/65.0628/-146.1627/2020/2080?format=csv

Closes #338

[BobTorgerson]

@cstephen Thanks for catching the permafrost year range and now the mmm values for the degree day and permafrost endpoints are including the year range in the file name and metadata too. Please have another look when you have an opportunity.