Change latitude dependence of critical daylength onset to is_cold_type PFT dependence

The current implementation of triggering for critical daylength for CTSM5.1 depends on latitude rather than plant type. It uses 15 hours for higher latitudes and goes down to about 11 hours. We think that it would be better if this was handled so that it was higher for arctic plant types (like needleleaf_evergreen_boreal_tree, needleleaf_deciduous_boreal_tree, broadleaf_deciduous_boreal_tree, broadleaf_deciduous_boreal_shrub, and c3_arctic_grass), This could be handled by adding a "is_cold_type" parameter on the parameter files that define the above list as .true. and others as .false.

This was originally suggested here...

https://github.com/ESCOMP/CTSM/pull/947#discussion_r402478089

@wwieder notes that the current implementation can be seen in plots with a line along latitude. As such this is something that should be fixed.

Because PFT's don't neatly fall into only high latitude or temperate, this will change answers and will need to be assessed scientifically.