Expose CodeMirror.operation() and replaceRange() on Document

[peterflynn]

Currently, it's hard to write a command that does text edits without talking directly to Editor._codeMirror, and we don't really want that. If we simply exposed operation() and replaceRange(), it would go a long way toward fixing this.

I'm fudging a little by marking this "code cleanup," but I think it would be a very simple change -- little more than proxying down to the matching methods on Document._masterEditor.

[peterflynn]

Nominating for sprint 8 since it ties in nicely with our extensibility goals

[njx]

Assigning to Peter, but let's talk about whether we want to expose the APIs or the object itself.

[pthiess]

moved to Sprint 9

[peterflynn]

Architectural discussion of this work is ongoing here: https://groups.google.com/forum/?fromgroups#!topic/brackets-dev/ok20uf8Q_a4

[peterflynn]

After discussion with NJ & Glenn, we decided to move this out to the beginning of Sprint 10.

[peterflynn]

Merged by pull request #980. Document now has equivalents to CodeMirror.operation(), replaceRange(), getRange(), and getLine(). (And Document.getText()/setText() have better semantics).