[#740,!427] Bumping library version numbers for 1.6.0-beta2

[#740,!427] Bumping library version numbers for 1.6.0-beta2

libkea_asiodns      -> no changes
libkea_asiolink     -> 7:2:0 (rule #3)
libkea_cc           -> 9:0:1 (rule #4,#5) Added BaseStampedElement class
libkea_cfgclient    -> 7:1:0 (rule #3) internal changes
libkea_cql          -> no changes
libkea_cryptolink   -> no changes
libkea_database     -> 3:0:1 (rule #4,#5) Support for Server objects
libkea_dhcp         -> 13:0:0 (rule #4) OptionDefContainer declaration changes
libkea_dhcp_ddns    -> no changes
libkea_dhcpsrv      -> 16:0:1 (rule #4, #5) ConfigBackendDHCPv* support for Server objects
libkea_dns          -> no changes
libkea_eval         -> 10:1:0 (rule #3)
libkea_exceptions   -> no changes
libkea_hooks        -> 7.3.0, bumped KEA_HOOKS_VERSION to 10
libkea_http         -> 6:0:1 (rule #4, #5) close_callback handler parameter added
libkea_log          -> no changes
libkea_mysql        -> 1:1:0 (rule #3) schema version was bumped
libkea_pgsql        -> 0:1:0 (rule #3) schema version was bumped
libkea_process      -> 4:1:0 (rule #3)
libkea_stats        -> 3:0:1 (rule #4,#5) Support for multiple data points per stat
libkea_threads      -> no changes
libkea_util_io      -> no changes, a Copyright year was updated
libkea_util         -> no changes, a typo in a comment was fixed
libkea_yang         -> 1:3:0 (rule #3)