fix looking up old transactions with non-ASCII names (broken in 0.18.0)

according to the documentation, SQLite's NOCASE collation affects only
ASCII characters. Unicode is explicitly mentioned as not supported.
Strangely Unicode still works on some Android versions/variants, but not
on others.

This change stops relying on NOCASE collation and puts back upper case
variant of transaction description in a new column, which is then used
when looking up previous transactions for auto-completion