Rename Project all_clusters method

This issue is a followup to this disscussion.

Project model class has confusing naming for clusters associations. Association returns not all clusters in relation with given project, but only those directly connected to it, and omits shared ones.

To address this all_clusters method was introduced. But it does not solve confusing name of mentioned association.

To mitigate confusing names they should be renamed:

1. clusters -> dedicated_clusters
2. all_clusters -> clusters