add implicit wait keyword

[TrN003]

This is about implementing access to the implicitly_wait function of the python appium client.

It would be nice to be able to specify an implicit wait. Explicit waits are an anti-pattern and avoiding them like this could de-clutter people's code.

I have written a minimal implementation here. To be specific, I added this function.
I would like to open a PR.

I have a few questions:

• how can I / should I build documentation
• should I add a mention of the explicit-wait anti-pattern in the documentation?
• the tests are failing on my end (3 pass, 17 failed). is this ok?

regards,
Nick

[TrN003]

@serhatbolsu ? any update on this?