Add action-chain-based click to pytest_selenium.click() instead of the current element.click()

This fixes the issue mentioned in #819 but not the issue in #827.

We first make sure that the mouse is moved to the right place and then just click - there is no checking for specific element present under the mouse pointer.
```
move_to_element(loc).click()
```
will move to the element and then click on it

while

```
move_to_element(loc)
ActionChains(browser()).click().perform()
```
will move to the element and then click on the current mouse location