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