lib: support 'personal' regexp, move to mu-contacts

Move the determination of "personal" to MuContacts; add support for
regexps (POSIX-basic, in //)

lib/mu-store.hh

@@ -96,8 +96,6 @@ public:
          * @return the metadata
          */
         const Metadata& metadata() const;
-
-
         /**
          * Get the Contacts object for this store
          *
@@ -105,7 +103,6 @@ public:
          */
         const Contacts& contacts() const;
 
-
         /**
          * Get the Indexer associated with this store. It is an error
          * to call this on a read-only store.
@@ -177,7 +174,6 @@ public:
          */
         bool contains_message (const std::string& path) const;
 
-
         /**
          * Prototype for the ForEachFunc
          *