When an agency uses Piwik to manage customers websites, there is often a relationship that one customer will have several websites.
It would be useful if Websites had a 'category' or 'group' attribute.
Then we add a new API to allow:
Other API changes:
(In ) Refs #2042 Adding SitesManager.getWebsitesGroups which returns the list of all website groups set
(In ) Naming consistency, not Websites but Sites refs #2042
We might do the UI changes in All websites (add the column) but for now it's enough