Prepare for ocrd_all release

[kba]

Some basic adaptions:

• method -> ocr_method
• ocr_method can be none, which is the default, which makes Froc only do font classification
• rename ocrd-froc -> ocrd-froc-recognize
• make replacing existing textStyle an option and the default

What is still missing are the tests, I've started on them but with all the other things to do, I don't want this to stop us from releasing in ocrd_all and improving later.

[kba]

Thanks for the review, I've tried to address the points in https://github.com/OCR-D/ocrd_froc/pull/9