Facet formatting for interactive (plotly) outputs

[JustinKurland]

Relatively minor issue, but an issue none the less. Currently all timetk plotting features work well for the static ggplot output as one can simply add the following, e.g.,

taylor_30_min %>% plot_seasonal_diagnostics(date, value, .interactive = FALSE) + ggplot2::theme(strip.background = element_rect(fill = 'red'))

However, in the event that one requires the interactive output, the same code with simply interactive=TRUE will produce a NULL output. More specifically,

taylor_30_min %>% plot_seasonal_diagnostics(date, value, .interactive = TRUE) + ggplot2::theme(strip.background = element_rect(fill = 'red'))

The solution requires going in and making the facet color accessible inside all the plotting functions within timetk. I am pushing the fixes for all the plots. Again, subtle change, but necessary to make changing the facets adjustable for those who may prefer something other than the theme_tq blue.