Support for group attributes and logical names

The main reason for this pull is to support expansion of grouped attributes like 

    KVALITET 1 2 * 5 6

In the process, I also translate the SOSI attribute names into their logical names according to the specification. This is not strictly necessary, I just think that they become more readable that way, especially for people who don't speak fluent SOSI. 

The translation table bloats the library somewhat, you might want to keep this in a separate branch if you want to keep a lightweight version of the library or don't like logical names. The actual size of the table can be reduced somewhat if turned into a single serialized JSON object.

There is also support for the BUEP geometry type, which can be pulled from kartverket:buep individually.