[WIP] get_share() to retrieve share information about known share (by id)

@PVince81: Any comments about this? (#7) Because I don't know if it's a right approach :wink: 
Here we should probably create a PublicShare if the share type is 3 (public share).

I'm still not 100% sure about the inheritance pattern here. Maybe it's simpler to just move everything into a single class (including token, file path, etc, even when not defined).

What do you think ?