Deal with StaleElementException in wait_for_element_displayed (and _not_displayed)
Update wait_for_condition to address StaleElementException
Update tests that use wait_for_condition to avoid StaleElementException
Pep8 fixes
Replace self.marionette with m where applicable
Merge pull request #787 from bobsilverberg/staleElement

Deal with StaleElementException in wait_for_element_displayed (and _not_displayed)