prepare new release

add date in changelog

Tag 20190221

Merge pull request centreon#1325 from CPbN/harden

Harden SNMP request even more

prepare new release (centreon#1208)

prepare new release (centreon#1186)

prepare new release (centreon#1158)

prepare new release (centreon#1104)

prepare new release (centreon#998)

prepare new release (centreon#973)