Added poll_frequency to wait_until_element and wait_for_ajax

When waiting for spinner or progress bar it's desired to have
increased poll_frequency rather than a default of 0.5 secs.

This may avoid high CPU usage seen while spinner or progress bar.

Also fixed few content view test-cases.
This:

    strategy, value = tertiary_menu_locator

is equivalent to this:

    strategy = tertiary_menu_locator[0]
    value = tertiary_menu_locator[1]

For example:

```python
>>> t = (1, 2)
>>> first = t[0]
>>> second = t[1]
>>> first
1
>>> second
2
>>> first, second = t
>>> first
1
>>> second
2
```

I'm not sure what to make of the Eclipse warning.