Add Option To Only Search Anti-Captcha Providers if Other Providers Fail To Get Subtitle

Since the Anti-Captcha/DeathByCaptcha providers cost $$, it would be nice to have an option to make it so that they are only searched if no suitable subtitles are found with other providers. This would save money (yes, it's only a small fraction of a cent per search, but it adds up over time), and make it more efficient as it would be fewer requests simultaneously.

The main reasoning behind this is I'm sure most people would prefer to pay only if they have to. If opensubtitles or podsnapi has a good enough subtitle, let's go with that. There's no reason to spend the money to search if there are free alternatives.