Replace typings with @types by npm

[chitoku-k]

What was a problem?

Some type definitions are out-of-date and the project didn't compile.

How this PR fixes the problem?

Remove typings and install npm's equivalent of packages instead.

Check lists (check x in [ ] of list items)

• [x] Coding style (if any code was modified)
• [x] Confirmed
  • OS: macOS 10.12.4
  • nvim version: 0.2.0

Additional Comments

It is made sure that the build has gotten rid of any errors and test scripts seemed to have run.

An ugly workaround is inserted into renderer/main.html due to an issue caused by the latest version of TypeScript (2.3.2). It would be better if removed.

See: javascript - Uncaught ReferenceError: exports is not defined in filed generated by Typescript - Stack Overflow

[rhysd]

I confirmed this works. Thank you.