Create Tools/Filter.hs
Implement isFilter and usageFilters
Filter.hs: implement getFilterPairs and isLikeFilter
Filter.hs: implement toFilter
Filter.hs: implement getFilters, mapToFilter
Filter.hs: Implement tryGetFilters

this will hopefully be the only exported function from that module
SQL: add a function to build SQL ADD string
Tools/SQL.hs: export buildSQLAdd
Add.hs: use Tools.Filter
add some basic tests