Split Bootstrap into "core/lib" and "cli" artifacts

[fboucquez]

Currently, if another tool or app wants to use bootstrap to manage a node, the symbol-bootstrap dependency will bring cli related dependency like oclif and inquirer. The "symbol-bootstrap-core/lib" library will need to externalize any prompt or confirmation function, this could be for example a UI screen, not a terminal one.

The repo will be the same, we most likely convert this project into a multi-module Lerna one. At least the "core/lib" and "cli" modules would be created, but it could be more.