Updated cluster list view

[a2batic]

• Remove the landing page with the create and import actions.
• Upon login, take the user straight to the cluster list view.
• Display imported and not imported clusters.
• Display any alerts related to the list clusters.
• Add a pop-up dialogue box, for each of the listed clusters, to show the cluster host list and any messages related to the specific cluster.
• Display basic utilisation or health information for imported clusters.

[nthomas-redhat]

Closing the issue as the related spec and PRs are merged