Replace babel with bublé

Pros of bubel over babel:

- No configuration (a la standard)
- Runs twice as fast, for quicker development
- Converts everything to ES5 (which is likely to be faster than ES6,
untested)
- Easy to swap Babel back in -- low commitment

Cons:
- Less battle-tested than Babel, but recommended by React core
developer so probably not too bad
- No babel plugin support, but we're not using that right now anyway.
Can switch back to babel if we need that later

BEFORE:

$ time npm run build

> webtorrent-desktop@0.16.0 build /Users/feross/code/webtorrent-desktop
> babel --quiet src --out-dir build

npm run build  3.07s user 0.27s system 115% cpu 2.902 total

AFTER:

$ time npm run build

> webtorrent-desktop@0.16.0 build /Users/feross/code/webtorrent-desktop
> buble src --output build

npm run build  1.38s user 0.16s system 114% cpu 1.343 total

src/.babelrc

@@ -1,8 +0,0 @@
-{
-  "plugins": [
-    "syntax-jsx",
-    "transform-es2015-destructuring",
-    "transform-object-rest-spread",
-    "transform-react-jsx"
-  ]
-}