React update

[abchilders]

Addresses #34. To merge this PR, please do the following:

• run npm install to install any new packages needed
• start up Autograder, log in, and browse through to make sure nothing important is broken :^)

--

If you have issues with npm install, it's probably from the fibers package, which react-scripts depends on. If you get errors, please follow the instructions for installing node-gyp. I'm on Windows 10 and I use VS 2019. I got an ENOENT error related to MSBuild.exe documented here; here's what I had to do to install fibers:

• npm install --global windows-build-tools in Windows Powershell, run as administrator. This will also install Python 2.7.
• install Visual C++ Build Environment 2019, making sure to use the "Desktop development with C++" workload AND check the "MSVC v141 - VS 2017 C++ x64/x86 build tools" box under that workload
• npm config set msvs_version 2017
• npm config set msbuild_path "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin\MSBuild.exe"

If you get an error about not being able to execute Python, make sure you have Python 2.7 installed and enter npm config set python python2.7.