[#4466] Added new SFLQ API funcs to PgSqlLeaseMgr

[#4466] Added new SFLQ API funcs to PgSqlLeaseMgr

/src/hooks/dhcp/pgsql/pgsql_lb_messages.*
    PGSQL_LB_SFLQ_POOL4_GET_ALL
    PGSQL_LB_SFLQ_POOL4_GET_BY_SUBNET
    PGSQL_LB_SFLQ_POOL4_GET_BY_RANGE
    PGSQL_LB_SFLQ_POOL4_DELETE delete
    PGSQL_LB_SFLQ_POOL6_GET_ALL fetch
    PGSQL_LB_SFLQ_POOL6_GET_BY_SUBNET
    PGSQL_LB_SFLQ_POOL6_GET_BY_RANGE
    PGSQL_LB_SFLQ_POOL6_DELETE
    - new messages

/src/hooks/dhcp/pgsql/pgsql_lease_mgr.cc
    PgSqlLeaseMgr::SFLQ_POOL4_GET_ALL
    PgSqlLeaseMgr::SFLQ_POOL4_GET_BY_SUBNET
    PgSqlLeaseMgr::SFLQ_POOL4_GET_BY_RANGE
    PgSqlLeaseMgr::SFLQ_POOL4_DELETE
    PgSqlLeaseMgr::SFLQ_POOL6_GET_ALL
    PgSqlLeaseMgr::SFLQ_POOL6_GET_BY_SUBNET
    PgSqlLeaseMgr::SFLQ_POOL6_GET_BY_RANGE
    PgSqlLeaseMgr::SFLQ_POOL6_DELETE
    - new SQL statements

    PgSqlLeaseMgr::sflqCreateFlqPool4()
    PgSqlLeaseMgr::sflqPickFreeLease4()
    PgSqlLeaseMgr::sflqCreateFlqPool6()
    PgSqlLeaseMgr::sflqPickFreeLease6()
    - added range adddress validation

    PgSqlLeaseMgr::sflqPool4GetAll()
    PgSqlLeaseMgr::sflqPool4Get(*)
    PgSqlLeaseMgr::sflqPool4Del()
    PgSqlLeaseMgr::sflqPool6GetAll()
    PgSqlLeaseMgr::sflqPool6Get(*)
    PgSqlLeaseMgr::sflqPool6Del()
    PgSqlLeaseMgr::sflqPoolGetCommon()
    PgSqlLeaseMgr::sflqPoolDelCommon()
    - new functions