kvdb+refactor: move all general sqlite code to seprate dir

In this commit, all the sql, non-postgres-specific, code is moved out of
the postgres package and into a new sqlbase package. This will make it
more easily reusable for future sql integrations.

kvdb/sqlbase/log.go

@@ -0,0 +1,12 @@
+package sqlbase
+
+import "github.com/btcsuite/btclog"
+
+// log is a logger that is initialized as disabled.  This means the package will
+// not perform any logging by default until a logger is set.
+var log = btclog.Disabled
+
+// UseLogger uses a specified Logger to output package logging info.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}