Clean logs on start - and eslint/mocha with code coverage (#1945)

* Clean logs on startup; install server-side testing/linting

* Add eslint config, make all of app/ conform to its demands

* Add Node.js testing and linting to CI

* Lock project to Node.js 7.9.0, used by Electron 1.7.10

* New eslint error: trailing commas in function argumensts

Node 7.9.0 doesn't like trailing commas, but Electron does

* Move electron to devDependency, tell eslint it's built-in

app/window_state.js

@@ -10,5 +10,5 @@ function shouldQuit() {
 
 module.exports = {
   shouldQuit,
-  markShouldQuit
+  markShouldQuit,
 };