Allow `screen.find` and other to work with non-image needles

**Short overview**
Currently `screen.find` is tuned to work on image data. 
However, this might change in the future to also allow non-image needles so the implementation should be flexible enough to allow for that.

**Use case**
Searching for other screen content besides images. Windows etc.

**Additional info**
It might break an API contract with existing plugins