Normalize the transactions DB

[ichorid]

Currently, some transaction data fields exist in multiple copies in the DB, e.g., transaction hashes used for addressing, etc. It poses two problems:

1. storing multiple copies violates DRY principle, which may lead to inconsistencies and errors
2. storing long fields (e.g. hashes) is less efficient in regards to space than storing just short keys

Before moving onward, we need to normalize the database.