add CHANGELOG

CHANGELOG

+## Centreon 2.7.3
+
+* Fix Recurent downtimes starting at 00:00
+* Fix search in Poller configuration page
+* Fix problems when sharing custom views
+* Fix description problem with custom macros containing dash
+* Fix time Interval change isn't being reflected in the polling Engine config 
+* Fix Missing GMT and UTC timezone
+* Fix No performance graph for host group service
+* Fix ACL were showing too much objects
+* Fix Impossibility to delete custom macros on service
+* Fix Split on multi graph
+* Fix Design on Monitoring Performances page
+* Fix CLAPI handled all broker parameters
+* Fix Custom macros can contain dash
+* Fix Time Interval change isn't being reflected in the polling Engine config
+* Fix UI doesn't display the good limit of pagination
+* Fix Some French translations were missing
+* Enh Improve listing possibilities in Widget configuration (Pollers and categories)
+* Enh Usuability of select2
+* Enh Possibility to reload several pollers in one time
+* Enh Add an API to send External Command
+
 ## Centreon 2.7.2
 
 * Fix eventlogs pages for performances and right for non admin users