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
replace sqlite3_prepare with _v2 calls

Should be ok for our usage
add sizegrip to finddialog
fix all warnings in the grammar and some bugs

literals were case sensitive so lower keywords broke parsing
improve the unittests for create table parsing
add method to easily remove fields from table
rework the dropcolumn function

it now uses the sqlb::Table object preserving:
not null, default value, check constraint