fix: minimize transaction duplicates

[fmaclen]

Prevent transaction duplicates by:

• normalizing transaction descriptions by removing white spaces (when creating, editing or importing)
• normalizing transaction dates to UTC at midnight (when creating, editing or importing)
• match existing transactions by matching key values: accountId, description, date and value (when importing)

[fmaclen]

These changes were included in https://github.com/Canutin/desktop/pull/131