Create a proper database upgrade method rather than dropping all tables

I changed the onUpgrade method from AntoxDB so the database adds just the new column instead of dropping the tables and recreating them.

I looked in previous commits to see what changes had been made from a version of a database to another.

There was a bug mentioned in #243 when the app crashed because there was no alias column in the table.
That was because the version wasn't changed (from 3 to 4) and the upgrade method didn't do anything.

I made sure that there will be no duplicates by checking if there is already a column in the table.

The current version of the database is 4.