Use local version of jQuery when in dev env

Allows people to edit/use local version of dillinger while not connected to
internet.
Highlight markdown blocks based on lang specified

This changes the logic so that the markdown block is highlighted when
there is actually a language prefix in the markdown block.

This will highlight in javascript:
```js
  console.log("sup?)
```

This will not highlight at all:
```
  Not Much
```
Merge pull request #204 from swang/highlight_based_on_lang

Highlight based on lang