Make CodeMirror editor prettier

- make line-height larger and font-size smaller to increase readability
- use pretty monospace fonts: Menlo on Mac OS, Consolas on Windows
- show 'text' cursor instead of 'pointer' when the mouse pointer is anywhere
  hovering the editor, not just over the text
- make caret more noticeable
Add word deletion shortcuts to CodeMirror editor

- Ctrl-Backspace/Ctrl-Delete deletes words on Windows
- Alt-Backspace/Alt-Delete deletes words on Mac OS
Merge pull request #3 from JetBrains/codemirror

Improve web demo editor style, add shortcuts