Replace logout/gravatar nav items with a more scalable dropdown menu

[bodom0015]

Problem

The mockups show a dropdown at the top-right of the navbar, but we currently have separate items. To add upcoming functionality, we should consolidate these navbar options.

Fixes #559

Approach

Replace "Logout" and User Gravatar items in the navbar with a more scalable dropdown menu.

How to Test

1. Checkout and run this branch locally, rebuild the dashboard
2. Login to the WholeTale Dashboard
   • You should see the navbar has a new "user" icon at the top-right
3. Click the "user" icon
   • You should see a dropdown expand
   • The dropdown should contain the user's first/last name and gravatar image
   • The dropdown should provide a link to the Settings page (to be added in a later PR)
   • The dropdown should provide an option to Logout

[craig-willis]

This looks fine to me. I did note a number of styling differences between the implementation and the mockup, but maybe this is due to us being behind several versions on Kristina's styling. What I noticed:

• Icon size and placement differ from mockup
• Icon highlight behavior doesn't match mockup
• Actual "user" icon is different
• There's whitespace around the selected menu item
• "Log Out" v "Log out"

Also, the dashboard failed to load because of a missing session route, which I resolved by merging user-settings-additional-accounts-view.

[bodom0015]

I am working off of https://wholetale.org/wholetale-css-mockup/src/settings.html, which I was recently told was the most up-to-date version of the mockups, and ignoring obvious differences like the background color.

• Icon size and placement differ from mockup - Yes, that is correct. The old UI had different margins and stuff for the navbar, and I feel that it would be very much out-of-scope to include that work here
• Icon highlight behavior doesn't match mockup - I'm not sure what you mean by this.
• Actual "user" icon is different - very minor, but happy to change the icon if it matters
• There's whitespace around the selected menu item - I can take a look at getting rid of the additional whitespace
• "Log Out" v "Log out" - "Log Out" is what it said previously... I'm not sure that this was even an intentional change, but whatever we want can be done

Regarding your final note, sorry about that - I seem to have forgotten just how fragile Ember is...

[craig-willis]

Sounds good. I'm not overly concerned about the styling, but did want to capture the noticed differences. Functionally all is good.

[bodom0015]

Closing this PR in favor of #563, since merging this would break the dashboard anyways.

All PR feedback has been addressed here, and those changes have been merged into the branch from #563.