Rewrite and simplify import SQL code

Rewrite the import SQL code using a similar method to the one used in
executeQuery(). This makes the code much easier to read and removes the
last remnants of that C code stolen from some demo application.
Allow CSV import into existing tables

Allow the import of CSV files into already existing tables if the number
of columns match.
Merge pull request #13 from MKleusberg/better-import

Better cvs import