Make SendEvent callable from all threads

This commit refactors the SendEvent call and moves it from the Input
ReaderBackend to to MsgThread. This allows all other types of threads
to access this functionality.

This necessitated a few more changes. Most importantly, one of the
ValueToVal methods was moved over to SerialTypes. Whereit arguably
belongs - there was nothing that was input-framework specific in
that method - and the functionality could come in useful in a number
of cases.

src/input/ReaderBackend.h

@@ -280,18 +280,6 @@ protected:
 	 */
 	virtual bool DoHeartbeat(double network_time, double current_time) = 0;
 
-	/**
-	 * Method allowing a reader to send a specified Bro event. Vals must
-	 * match the values expected by the bro event.
-	 *
-	 * @param name name of the bro event to send
-	 *
-	 * @param num_vals number of entries in \a vals
-	 *
-	 * @param vals the values to be given to the event
-	 */
-	void SendEvent(const char* name, const int num_vals, threading::Value* *vals);
-
 	// Content-sending-functions (simple mode). Include table-specific
 	// functionality that simply is not used if we have no table.