add "Brackets" to user agent string, and move remote debugging port to config.h

Fix for adobe/brackets#2213

Modifies the user agent string to include "Brackets". The user agent string now looks like:

```
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/537.1 (KHTML, like Gecko) Brackets/0.19.0.0 Safari/537.1
```

For bonus points, also moves the hard-coded remote debugging port to a #define in config.h. By having it in config.h, we can set separate ports for Brackets and Edge Code. This means that we can debug both of them at the same time without having to worry about which one we opened first.