Fix Charm#reset when running on iTerm

For some reason, iTerm doesn't support resetting the screen using `0x1b63` – the builtin `reset` command even outputs "!p" instead of clearing the screen.

By also using the `[2J` escape code, we can ensure that the screen is still reset correctly on iTerm and any other terminals that may not support `0x1b63`.

This issue affects workshopper too – screenshot:

![screen shot 2014-02-18 at 11 13 48 am](https://f.cloud.github.com/assets/569817/2190827/5d959224-9833-11e3-93ad-235d253b9c35.png)