Move gganimate to Imports

[aravindhebbali]

Current Behavior

User installs the rfm package, gganimate is not installed as it is not included in Imports. When any of the below functions are called with the animate argument set to TRUE:

• rfm_plot_segment_summary()
• rfm_plot_segment_scatter()
• rfm_plot_revenue_dist()
• rfm_plot_median_recency()
• rfm_plot_median_frequency()
• rfm_plot_median_monetary()
• rfm_plot_order_dist()

the package checks if gganimate is already installed. If yes, it generates the plot, else, it prompts the user to install gganimate.

New Behavior

Move gganimate to Imports. This ensures that the user need not be bothered to install gganimate if its not already installed.