See https://github.com/jenkinsci/acceptance-test-harness/pull/631 and https://github.com/jenkinsci/acceptance-test-harness/pull/632.
 
As part of those PRs I've found that many classes extending `PageObject` are using the constructor receiving `Injector` as parameter. This constructor should be deprecated and those classes should use the other constructor receiving the `context`.

Motivation of the change

• If more than one instances are involved in the test (SSO e.g.) using the first constructor makes the injector retrieve the Jenkins instance, and it always retrieves the first one registered.
• Using the constructor with `context` stores the injector as well, so we don't lose anything