Improve PDF export to be able to select one from a set of fonts installed to Confuelence

Currently, only a single custom font is supported.

But in a multi-language environment, users use different language on one site. For exsample, CV is a common page in personal space, these CVs maybe in different language for different purpose, somtimes in english, sometimes Japanese or Chinese.

So if PDF export can install multiple fonts, and one for default, when user export content, he/she can use default or select font from a list, that'll be appreciated.