This is a piece for #18, we need to retrieve paginated transactions for a given
address.
NOTE: This commit doesn't include tests in order to work in the frontend
concurrently, tests will be included before the release.
The trait is implemented by TransactionPostgresDataHandler and
TransactionPostgresDataHandler.
This is a piece for creating endpoints interacting with transactions
from the database instead of the xsn service.
When a block is processed, in case it can't be fully retrieved from the
rpc server, the block is ignored.
When a block is processed, if there is an existing block having the same
height, it will be replaced by the new one.
This is a part for fixing the bug #6
Alexis Hernandez