configured eslint to work on ts files

[TClark1011]

ESLint now uses the @typescript-eslint parser to parse .ts files. .js files still use the default parser. This was done by using the overrides key in the eslint config to set the parser specifically for .ts files.

NOTE: I did not lint any files as part of this PR. My recommendation would be that if the eslint setup in this PR is approved, then a second commit should be made where all the ts files in the codebase are linted, and possibly also have prettier run on them.

Closes #472

[angus-c]

Thanks!