Add Grouping to equations

[kjacobsen16]

Pete would like some sort of grouping number for the DA only equations and things like that

@USGSPMM3 can you expand on this a little, or point to an email chain where I can get more info?

[USGSPMM3]

Issue: if two different equations are used to solve for the same flow statistic label, we are having issues with the weighting. The specific example in Iowa was that we have equations to solve for PK100 (renamed) using all BCs and equations to solve for PK100 using DA only. When the basin falls into two different regions, the weighting doesn't work correctly. We have temporarily addressed this by using an alternate PK100 stat label.

Potential solution previously discussed: We need to add a new attribute into the Database that is a group number and then weighting is only done among equations with the same group number. Equations of the same type and author would get a unique group number. Most of the time (~95%) we don't have issues but this will allow us to not create or put equations into other stat labels when they really belong in the "standard" stat label.