Abe404/root_painter: 0.2.17

In this release a bug is fixed with the metrics plot that allowed the first 6 points (the clear examples) to be highlighted as selected, even though those points are otherwise not visible in the plot. They are excluded from the plot as corrective annotation metrics are not possible to obtain on these images as, if the protocol is followed, these initial images will not have been annotated correctively.

The caching mechanism has also been altered to using a single pickle (.pkl) file for all images. This change was made because on some network file systems (for example SSHFS) just checking the existence of many files was fairly slow for larger projects.