[plugin.action.sendKey] add keyboard mapping to replace \uE003 by something readable

[rodneyrehm]

We want to add a keyboard map that translates "special keys" like keys.backspace = '\uE003' (up, down, enter, esc, page-end, …).

Maybe we can use unicode-keymap?

This may also help other keyboard-related actions. The question how this should be made available to the test. It could be as simple as var map = require('dalek/key-map') in every test that needs it…