Implement essential subscriptions functions * Look for projects with monitor enabled on plugin load * Keep track of manifest repos that has subscription enabled * Keep track of projects defined in manifests being monitored * Update when project.config is changed * Update when manifest changes * Update on project changes (for projects in manifests being monitored) * Repo where generated manifests are stored will not be monitored Change-Id: I63c749487f52c58d20ce8004bdb892ae4b78afd6