Update dependencies in package.json

[hangler]

Fixes #178. Removes a number of unused / unneeded packages, and updates a number of others. This should also address a number of security issues from outdated dependencies.

After a yarn install, /ClientApp should build (yarn build) with no warnings or errors.

In a few cases, I had to use FixTypeLater (an alias for any) for the sake of expediency when dealing with third-party libraries which do not have readily-available built-in typings. At some point we can try to use better typings.

[hangler]

Going to run an npm audit to see if there are any more packages that can be updated.

[hangler]

The only remaining vulnerability is this one, which is almost certainly nothing to worry about, according to the Create React App team (see also Stack Overflow):

% npm audit
# npm audit report

nth-check  <2.0.1
Severity: high
Inefficient Regular Expression Complexity in nth-check - https://github.com/advisories/GHSA-rp65-9cf3-cjxr
fix available via `npm audit fix --force`
Will install react-scripts@2.1.3, which is a breaking change
node_modules/svgo/node_modules/nth-check
  css-select  <=3.1.0
  Depends on vulnerable versions of nth-check
  node_modules/svgo/node_modules/css-select
    svgo  1.0.0 - 1.3.2
    Depends on vulnerable versions of css-select
    node_modules/svgo
      @svgr/plugin-svgo  <=5.5.0
      Depends on vulnerable versions of svgo
      node_modules/@svgr/plugin-svgo
        @svgr/webpack  4.0.0 - 5.5.0
        Depends on vulnerable versions of @svgr/plugin-svgo
        node_modules/@svgr/webpack
          react-scripts  >=2.1.4
          Depends on vulnerable versions of @svgr/webpack
          node_modules/react-scripts

6 high severity vulnerabilities

To address all issues (including breaking changes), run:
  npm audit fix --force