Add to Options - Plotting the ability to set default font size and types

[jsnel]

A user asks:
I am using Glotaran, just wonder how to change the font size? I found the layout of the streak camera images in Glotaran is quite nice, should be good for publications, but the font size for axies is too small,

My reply:
I was planning to add this to the Options - Plotting panel - the ability ot set global font size for all plots
then we just need to modify the code where the plots are set and read from a property, and if it doesn't exist assume a default.