Organising dashboard with private / shared permissions

[rmehta]

Once there are too many dashboards, the homepage is a problem. To solve this, here is a proposal:

1. Every dashboard should be private by default
2. You can make a dashboard "shared" (global, or maybe shared with a specific set of users?)
3. Create 3 tabs on home page "My Dashboards", "Shared", "Public"
4. I should see my dashboards in the first tab
5. Shared private dashboards on the 2nd tab
6. Public dashboards on the 3rd tab