move to Freedom v0.5-based freedom-for-xxx providers

This moves to Freedom v0.5-based `freedom-for-chrome` and `freedom-for-firefox`. No minor version bump since this doesn't require an API change. My next task is to give `socks-rtc` a custom API; that would obviously be a breaking change and should bump us to v0.2.

Tested with `grunt endtoend` and with curl in both Firefox and Chrome.

Only issue I see are some error messages in Chrome:
```
```

I wasn't able to quickly track down the source of these. Since my next task is to give `socks-rtc` a custom API, I intend to track down the issue then. All seems to work fine; my guess is this error reporting is new in Freedom 0.5.