stbt-record: Replace multiple wait_for_matches with a press_until_match

If the user presses the same remote control key multiple times, then
insert a single `press_until_match` call to the output file instead of
multiple `press` and `wait_for_match` calls; and save a single template
image after the last keypress.

Example: instead of
```py
stbt.press('OK')
stbt.wait_for_match('0001-OK-complete.png')
stbt.press('OK')
stbt.wait_for_match('0002-OK-complete.png')
```
have
```py
stbt.press_until_match('OK', '0001-OK-complete.png')
```