Feature/frontend auth

[nbarlowATI]

First iteration of frontend work for authentication.

• Login, Logout, Signup components, and associated Routes.
• Buttons added to homepage for login/signup (if not logged in) and logout (if logged in).
• Link added to Navbar to logout (if logged in), and CaseSelector not shown if not logged in.
• Redirect to login page from e.g. /case/1 or /case/new if not logged in.
• Send API requests with authentication token in header.

[coveralls]

Pull Request Test Coverage Report for Build 2331746311

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 87.688%

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Totals
Change from base Build 2313964252:	0.0%
Covered Lines:	876
Relevant Lines:	999

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💛 - Coveralls