Plottoolbox

Fix

- fixed secondary_y option for the time plot

Feat

- added dropna option to all plots
- **waterfall**: added new waterfall plot but not particularly impressed - WIP

Feat

- finished target and taylor plots including tests

Refactor

- moved SkillMetrics and SciencePlots to use from git submodules
- removed unused os imports

Feat

- added hexbin plot

Fix

- fixed cltoolbox so not part of imports