Spaces in table, index and field names are actually allowed by SQLite,
so no need to check for them.
However, "`" characters cause problems when appearing in SQL statements
so disallow them instead.
Allow setting the default value, the check values and under some
circumstances the not null flag when editing existing tables.
This required some changes to DBBrowserDB::renameColumn() which is now
using some more features of sqlitetypes.cpp but could still be improved.
Do just the same in the ImportCsvDialog as before in the
EditTableDialog, i.e. using a unique savepoint name which is not
released when the import was successfull.
Rewrite the dialog to import CSV files using a Qt Creator form file.
Simplify the CSV import a little bit.
A bit unrelated, but needed for this anyway:
Create the restorepoint right after opening a database file instead of
just doing so after the first change.
