Add "limit" argument to methods that return or click multiple elements

Add "limit" argument to methods that return or click multiple elements.
Updated methods: ("0" means no limit)

• self.find_elements(selector, by=By.CSS_SELECTOR, limit=0)
• self.find_visible_elements(selector, by=By.CSS_SELECTOR, limit=0)
• self.click_visible_elements(selector, by=By.CSS_SELECTOR, limit=0)

Example:
self.click_visible_elements('[type="checkbox"]', limit=5)
(Click the first 5 visible checkboxes on a page)