Allow one to browse lines or selections from an editor

This pull request stems from our conversation about #883; a Helios user should be able to browse a selection or line from an editor. It's superficially similar to the `Finder` that you created (and uses some features from it), but I think that my implementation provides a better migration path from the old IDE because: 

1) Users will still use the same name: `Browser`. The old IDE browser has been renamed to `IDEBrowser`, so there won't be any naming conflicts.
2) @herby pointed out that instances of the old IDE Browser were created via `new`. The new Browser service also supports calling `new`, and will just delegate to its implementation while indicating that one should use `open` or `openOn:` instead.

Here are some other features that are supported in the Helios Browser; they have not been ported to the old IDE Browser, but I'd be happy to do so if there is demand:

* A selection or line can be browsed by pressing the `BrowseIt` button in an editor, or pressing `Cmd-B` on a Mac or `Ctrl-B` on a PC.
* The selection or line to be browsed will be evaluated first (think `DoIt`), and the class of the resulting object will be browsed.
* Instances and classes can be browsed. In the case of an object instance, its class will be browsed.
* If a selection or line cannot be evaluated it will be opened in a `References` browser. The only instance in which this does not work is if the selection or line has an underscore. This appears to be due to #20, and I'm not sure how to fix it yet.