This commit adds eslint support for .ts and .tsx files.
The recommended Typescript rules are applied only to .ts and .tsx files
and not to existing .js or .jsx files. This is accomplished by creating
a separate .eslintrc-typescript.yml file and pointing to it in the
.eslintrc.yml overrides parameter.
A .eslintignore file was added. This file has syntax similiar to
.gitignore and is used to ignore the programatically generated API
slices so that we do not have to deal with a massive diff whenever we
update one of them.
