break out creation of 'WHERE MEMBER OF...' statements into seperate function...

... in order to allow adding additional expressions to disjunction if necessary.

Using this change to allow disjointed filter expressions for Program list when filtering by various Coverage area options. I was originally going to allow an additional optional array of expressions to be added to addWhereMemberOfFilter() that would be array_merged before joined together into the disjunction. Instead I decided to break the creation of the "WHERE MEMBER OF" expressions into another function and merge in any additional expressions myself in program search.