Conditional root paths

[crawfoal]

Description

• the logo in the app bar now links to the root path
• the root path now depends on the user - for admins, it is the admin dashboard, for regular users, it is the regular dashboard, and for visitors, it is the welcome page
• for admins, the link to the admin dashboard was removed because now they can access this by clicking on the logo; instead, they now have a link to the user dashboard

Fixes #169 Fixes #170

Developer Checklist

• [x] I have read and followed the contribution guidelines.
• [x] All specs and linters pass (including Code Climate)
• [x] I have followed the style of nearby code
• [x] The build on Semaphore is successful
• [x] I have added tests for my changes.
• [x] I have gone through my changes by hand, either in the browser or terminal, which ever makes sense

[crawfoal]

I forget - are you waiting for something from me on this?

I feel like there was somewhere where you pointed out that I should add a test or two, but I can't find the comment.

[pierce-m]

Hi, no i just had asked about the way the tests read, it reads like a logged in user should not have a link to the user dashboard while a logged in admin should. But that's more for my own understanding, I believe I approved this pull request when I reviewed it a couple days ago.