Share album with other Blockstack users

[nerdic-coder]

Make albums shareable with other users.

When on Album page add a share button in edit mode. When clicking the share button a dialog shows up where you can enter username, and toggle for read only or if the user should have both read and write permissions.

The shared albums should also have an icon indicating that it shared, when clicking the icon show the list of users you share it with.