Implementing most of functionalities on Linux

[LangArthur]

Hi !

I do not know if the project is abandonned or not, but I noticed the linux part was empty, so I did most of it.

I kept the original ShowFontPanel, since I am not 100% sure about what you wanted to achieve here and if it already work (or not).

Also, I used the FontConfig library for getting the fonts. It seems widely spread across linux distributions but I cannot confirm it.

I did not implemented all the traits in the GetAvailableFonts method, since I am not sure to understand all of them. I would be glad to know more about them ! At the moment, here are the missing traits :

• compressed : may it be fonts with width less or equal to 50 ?
• fixed pitch
• narrow : as far as I went, I understood it is linked to spacing between each character. But at which level is it consider as narrow ?
• non standard charset : I understood what was a charset, I just don't know when a charset is standard or not.
• poster
• smallCaps : I saw some example of small caps fonts, but I have no idea about how to detect them.

I am also open to changes, if there are problems.

By the way, I added some additional tests.