Remove missings from tables

[strohne]

Default parameter in descriptive tables should be: no missings. Can the number of missings be printed below the table?

[strohne]

Maybe already solved - check whether all tables (that have missings) have a missings column / row behind the totals.

[strohne]

In the data_rm_missings and data_rm_negative functions:

• Add the column name in the message and whether values were removed for a plot or a table.
• Add the information to the resulting volker tab or plot as an attribute (that later can be printed below the output)