Closes #3172

https://github.com/codemirror/CodeMirror/issues/3205

Issue #3117

Issue #3095

(Blint is the in-tree tool factored into its own npm package.)

Issue #3023

Issue #3009

- line.handle.gutterClass is successfully
- Gutter class is removed from Markup

Amending removeLineClass to remove gutter class from markup.

Issue #2995

Issue #2263

See http://discuss.codemirror.net/t/loadmode-js

I'm rewriting the way that visual mode is written to:
1. Fix some tricky bugs, like https://github.com/codemirror/CodeMirror/issues/2913, and a couple I uncovered while doing this. (Unit tests updated)
2. Significantly simplify blockwise visual mode

The core of the changes here is that I'm creating a vim selection model. The selection model consists of

```
vim.sel.head
vim.sel.anchor
vim.visualMode
vim.visualLine
vim.visualBlock
```

I'm creating a 2-way binding between the vim and codemirror selection models. All motions now rely only on the vim selection model. Operators and actions still rely on the codemirror selection model, since they operate directly on the text.

Sorry for the gigantic change but I couldn't make it any smaller and still pass all the tests... I'm planning to delete `getSelectedAreaRange`, `getLastSelectedAreaRange`, and `selectBlock` in future changes as they are obsolete now that vim keeps its own selection model.

An added bonus here is that visual line mode now has a cursor that can be moved.

Add tests

Issue #2908

As long as CodeMirror.normalizeKeyMap is called on them before they are
used. This interface is a little weird, but backwards-compatible.