API change: easy_plot_title_size should be called easy_title_size etc

[davidhodge931]

I think the use of "plot" in function names is unnecessary, makes the function names too long, and be more difficult to find/guess the function name for new users.

E.g. I want to remove the title or subtitle. I wouldn't even know that that is called a plot.title or plot.subtitle in ggplot2 language. The teach = TRUE can tell people what this is in ggplot2 language.

So I think that easy_plot_title_size should be called easy_title_size instead - with the former deprecated.

This applies to the following functions: