Objects.isNull is only available from jdk 1.8 but apollo-client is targeted to jdk 1.7+, so we need to use a compatible one (#2677)

fix delete children clusters twice.

* fix setting value of property in xml is null throws NullPointerException

* fix setting null value of property in xml throws NullPointerException

This reverts commit 437026f3.

* init i18n support

* polish translations and fix some bugs introduced

* refactor app namespace duplicate message

* fix non-properties namespace display issue

* add cluster open api client
* add toString for open api dtos
* add rollback release open api

java client's long polling timeout is 90 seconds, so server side long polling timeout must be less than 90 (#2630)

fix the issue that project owner cannot manage application master even if role.manage-app-master.enabled is turned off (#2627)

openapi support create and load cluster info

* configure server side's long polling timeout

* logical update

* Revert "logical update"

This reverts commit 99943df3

* logic uapte