fix: various small navbar fixes

[bodom0015]

Problem

The "Data Catalog" and "Compute Environment" links just contain static placeholder data.

Approach

Hide these links for now until these views are functional and add more value to the platform.

Fixes #97 - Hide the links until these views are finished

Other minor fixes on this branch:

• Fixes Task viewer takes up button real estate #84 - Adjusted notification stream margins so it no longer overlaps with the navbar
• Added missing User Guide link to the navbar (clicking icon previously did nothing)
• Display avatar in the navbar when available, disabled menu item for avatar/username, as clicking it currently does nothing

How to Test

Prerequisites: none

1. Checkout this branch locally, rebuild the dashboard
2. Login to the WholeTale Dashboard
   • You should see only "Tale Dashboard" in the navbar
   • You should not see "Data Catalog" or "Compute Environments"
   • You should see your gravatar displayed in the navbar, if you have one set
3. Expand the Notification Stream panel
   • You should see the placeholder text for the notification stream is slightly more centered
4. Expand the user dropdown and hover over your name
   • Your cursor should not indicate that this item is clickable
5. Click the (i) symbol in the navbar
   • You should be brought to the User Guide