Fix a few bugs in the CSV import

Start numbering the rows in the preview table view of the ImportCSVForm
with #1 instead of 0.

Don't create too many columns when filling the preview table view.

Keep the UI responsive when reading a CSV file. This way the progress
dialog can be seen, too.

Don't crash when reading files without an empty line at their end.
Set text codec to UTF8 fixing the handling of special characters

Set the encoding used by Qt to UTF8. This fixes the wrong appearance of
special characters caused by SQLite using UTF8 and the application
ISO-8859 or whatever.
Partially undo 9a9d32a5a7bfdb5d26eb21ce4890bf235a06357a

Reload the DB structure even when changing to the browse tab asthe
structure might have been changed when coming from the SQL tab.
Make sure to always escape table and column names properly

Always put `...` around the names of tables, columns and other objects
to avoid errors when the user creates objects with the name of key
words.