Leverage WebDriver built-in implicit wait

[tristanlabelle]

We've been emulating implicit wait functionality by repeated requests when webdriver offers it as a built-in mechanism. Using the built-in mechanism when available has the advantage of making logs less verbose. This change preserves the repeated request emulation mechanism as a fallback.

This change aligns better with web driver concepts. We use "implicit wait timeout" instead of "default retry timeout", and make it only apply to findElement, introducing a separate "implicit interaction retry timeout" for interactions (which is not a webdriver protocol built-in functionality). The implicit wait timeout now defaults to 0 seconds, as per spec.

Individual operations still offer to specify a wait timeout, and this is implemented by temporarily changing the implicit wait timeout, since that is the only mechanism offered by webdriver.

[jeffdav]

Looks good, I think. I would maybe update the README to talk about the various timeouts and how they interact?

[tristanlabelle]

@jeffdav good call, I updated the readme.