RFE: allow checking for element enabled/disabled status

For a test case I'm currently working on [1], the only way I found to check for an element's enabled/disabled status is to query the private `_element` attribute directly:

find_by_id_result.first._element.is_enabled

Would it be reasonable to add an API equivalent to the existing one for `visible` that instead checked the `enabled` status of the underlying component? (I have a partially prepared patch for this, but I'm having trouble running the test suite locally on Fedora, so it isn't complete yet, and I figured it made sense to ask if the idea was acceptable in principle before continuing to work on it)

[1] https://github.com/leapp-to/prototype/pull/139/files