Queries shoud store some execution information #50

Query execution fetches quite a bit of data and meta data that is then available behind the scenes and is used by the output transformer to create the pandas data frame with the results. It might be beneficial if some of this information, particularly the meta information, is stored inside the query
object internally.
This would enable several things. First of all one could build functions for the user displaying her the meta information for the specific query, like the short descriptions of the used statistics and the descriptions for enum output fields.
Another advantage would be in view of future features that conditionally format the output of a query based on arguments. (Speaking column names and descriptions instead of enums). If the query results are stored internally such conditional formatting could be reconfigured and applied without rerunning the query against the API. For example if I first want to display the results of a "WAHL09" query with the column name "Zweitstimmen (WAHL09)" instead of "WAHL09" but later change my mind towards the shorter description.