Adds an rcparams configuration for plotting

This enables users to configure the latex setup to meet there needs. I've added some documentation in an FAQ style to enable it and used the dosctring for documenting exact details. Please take a look at the docstring to see how this operates in practice. Comments/suggestions on the choice of defaults are welcome.

cc @marc.arene @matthew-pitkin @colm.talbot @moritz.huebner as I know you all have an interest in this.