Set default selector to ``html`` for text-search methods.

Set default selector to html for text-search methods.
(It's also optional now.)

Now you can do something like this:

self.assert_text("SOME TEXT")

instead of this:

self.assert_text("SOME TEXT", "html")

(Default selector type for selectors: by=By.CSS_SELECTOR)

Methods effected:
assert_text
is_text_visible
wait_for_text
find_text
delayed_assert_text
wait_for_text_visible
assert_text_visible

Due to keeping backwards compatibility, a few older methods remain that do the same thing as newer methods. (Method names were shortened from their previous versions.)