Update FontAwesome class, also make more open to extension

[fancellu]

e.g. no Database

https://github.com/henrikerola/scaladin/blob/3.2/addon/src/main/scala/vaadin/scala/server/FontAwesome.scala

http://fortawesome.github.io/Font-Awesome/icon/database/

Having FontAwesome.apply private makes creating own glyphs a bit annoying

Thanks.

[henrikerola]

Updated constants are there now. Need to see how to open it for extension..