Rely on actual project list for selection of default project

[edlerd]

Done

• Rely on actual project list for selection of default project
• fix invalid object access for restricted users

Fixes #575

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @lorumic or @edlerd for access.
   • With a local copy of this branch, run as described here.
2. Perform the following QA steps:
   • try access to the UI with a restricted user (lxc config trust list then lxc config trust edit $id then change restricted: true and add a project which is or is not the default project)
   • The restricted user should be redirected to a project they have access to (i.e. non-default) when opening the /ui url in a browser.

[webteam-app]

Demo starting at https://lxd-ui-582.demos.haus

[mas-who]

QA'd locally with the changes since I can't ssh into the demo server node yet. LGTM with just one small nit comment.