Rethink image matcher interface

[KilianB]

We deal with configured image matchers that have a float value associated when adding algorithms (Single Image Matcher , Database Image matcher) and matchers that do not have a preset in the same sense (cumulative image matcher and random forest matchers).

Maybe it's time to refactor the image matchers and introduce a new abstract class in between the interface and the implementations.

also move from float threshold to double precision, This will be yet another breaking change. Bump version to 3.0.0

#16 should be resolved in the same patch if major version is bumped.

[KilianB]

Upgrade to double precision 65188a7

[KilianB]

fixed with v 3.0.0