Experimental removal of WhenPresentDecorator.

Hi there.. this PR isn't for merging.. but more of a question as to a design choice.

The only benefit I could think of for WhenPresentDecorator would be using it like..
```
element = browser.checkbox.when_present
element.double_click
element.right_click
# .. some more actions or assertions
```

But considering without the delegating until later it would bomb out at the #when_present anyway the `element.hover` and `element.right_click` would never be called anyway?

Hmm.. I guess if the double_click made it disappear..

Just thought you might be able to shed some light!