Consider migrating visualisation tools to graphics specifics package

[mitchelloharawild]

This package contains both data visualisation tools and features/statistics for time series. These goals can be somewhat conflicting. Feature extraction tends to require highly performant code with minimal dependencies, while the visualisation goal introduces several large package dependencies.

Considering the package name 'feasts' and its meaning 'Feature Extraction And Statistics for Time Series', I believe that the plotting tools available in this package would be better suited in a different package. It would be possible to provide a gradual migration to the new package, and so these changes will not be breaking changes.

A potential recipient for the visualisation functions is {gravitas}. If the plotting tools are moved to this package then the scope of {gravitas} would be increased.

Just a thought for now, discussion is encouraged - @Sayani07 @robjhyndman @earowang @dicook

[mitchelloharawild]

The decomposition methods in this package are less problematic as they can be (and are) used for calculating features. Additionally they have lighter package dependencies, or have dependencies listed as Suggests.