add emptyinsertstm function to table object

creates an empty insert statement for the table fields
add a bit of documentation sqlb::Table::sql()
Rework the kinda broken add record button

Now it should always be possible to add a new record,
no matter how the table is defined or what the new data default is.
The default new data setting will be removed in the next commit.
remove the defaultnewdata setting

it is useless now
show why we couldn't update the record
forgot to update the error message of add record
make the empty insert statement work in pk + not null situations
fix the windows build
kill too long lines, no functional changes
don't insert nulls into columns with a default