Introduce structs/interfacess for new storage units

This commit simply splits the interfaces but introduces no new structs

     - Introduce the QueryPackStore, mrvacommander/pkg/qpstore
     - Introduce the CodeQL database store, pkg/qldbstore/interfaces.go

pkg/qldbstore/interfaces.go

@@ -0,0 +1,6 @@
+package qldbstore
+
+type DBLocation struct {
+	Prefix string
+	File   string
+}