- don't remove parentheses around subqueries
   (without the parentheses, it is not valid SQL)
   * when saving a Field (name value) typed by the user interactively
   * when parsing SQL and constructing the initial Query Design view

 - automatically add the necessary parentheses
   when a SELECT statement is entered as column name

Also:

In code saving a Field (name value) typed by the user interactively,
factorise some common code

Assorted minor fixes (typos in comments, etc)

Change-Id: I3843258323c903cba23238b0730ec4eb5875f792
Reviewed-on: https://gerrit.libreoffice.org/1827Reviewed-by: Miklos Vajna <vmiklos@suse.cz>
Tested-by: Miklos Vajna <vmiklos@suse.cz>