Log additional information on start/end of validation cycle.

Log additional information on start/end of validation cycle.

+The information is printed at INFO level:
- When a client starts/ends a connection, or when the connection is killed (print its address and an internal ID).
- When a new validation cycle is started and finished (includes number of valid ROAs and Router Keys, current/new serial number, and real execution time).
+Update function 'log_debug_enabled' and add 'log_info_enabled' function.
+Add functions to get total ROAs and Router Keys from db_table struct.