Feature/typescript validation

[chandlerprall]

Adds linting rules for TypeScript and runs tslint & tsc type checking on the existing lint / lint-fix scripts. Verified both linting and type checking detects problems in src directory.

Fixes existing TS compilation error in the EuiBadge's definition.

[chandlerprall]

jenkins test this

[snide]

@chandlerprall What's the best way to test this? Just screw up some of the definitions?

[chandlerprall]

@snide yeah; I also used a dummy.ts file in src/components to test some invalid type usage, like

function add(x: number, y:number) {
  return x + y;
}

add(4, '5');

changing the '5' above to "5" should also demonstrate the linting

[snide]

I gave this a run locally and seems to work. I'm likely not the best candidate for testing, but it works how I'd expect.