Add a "when clause" to the keybindings in VS Code

[nachocab]

To avoid conflict with other VS Code extensions, a when clause should probably be added to the default keybinding.

Something like this:

{
    "key": "ctrl+cmd+space",
    "command": "neo4j.runCypher",
    "when": "editorTextFocus && editorLangId == 'cypher'"
  }