Introduce data objects for Table / Column

Hey,

I am currently trying to serialize the `table_map` to a file. The thing is the table_map consists of `TableMapEvent`s, which makes it rather hard to get a good serializable Object.

Therefore I thought that it would be nice to have a Table-Object, similiar to the Column-Object, which just holds the data. I also used a seperat dict (`self.data`) instead of `self.__dict__`, which again makes its easier to seriale and compare the objects based on the data.

What do you think?

Thanks in advance
Björn