- Collected in animate_options.R
- Sets global defaults in plot_settings environment
- Adds ability to set animation options, similar to theme_set() from ggplot2
- Adds getters for current (if set) or default animation options

Merge branch 'pkg-add-anim-options-merge' into pkg-add-anim-options

# Conflicts:
#	NAMESPACE
#	R/animate_tidyr.R
#	R/plot_helpers.R
#	man/anim_options.Rd
#	man/animate_gather.Rd
#	man/animate_spread.Rd
#	man/static_plot.Rd

Currently only used for setting global text and title font sizes, but can be extended to other options that we may wish to set for more than one plot. For fonts, we now provide `set_font_size()` that can be used to set text and title sizes across all subsequent animations. Includes internal getter functions get_{text|title}_size().