Turn chasquid-userdb into chasquid-util

This patch removes chasquid-userdb and adds a more generic and extensive
chasquid-util, that supports various operations on user databases as well as
aliases lookups.

The code is not very pretty but for now I took a more practical approach, the
tool is ancillary and can be tidied up later.

internal/aliases/aliases.go

@@ -69,11 +69,11 @@ type Recipient struct {
 	Type RType
 }
 
-type RType int
+type RType string
 
 const (
-	EMAIL RType = iota
-	PIPE
+	EMAIL RType = "(email)"
+	PIPE  RType = "(pipe)"
 )
 
 var (