Move nestcolor from suggests to import

[shajoezhu]

          I don't really want to drop "nestcolor::theme_nest()" from the g_lineplot default option, reason being this is primarily used by roche, and the nest default values are set for a reason, 

I don't want to replace the usage of nestcolor either, feel like this is going backwards, and adding code that we have to maintain in tern ...

one possibility is to move nestcolor from suggests to import @pawelru @khatril , what do you guys think?

Originally posted by @shajoezhu in #1293 (comment)