Add wallet fragmentation check

[arobsn]

As described in #165, the old and UTxO count verifications are very inefficient and expensive.

The old UTxO check was optimized in #175, but unfortunately addresses { boxesCount } suggested in #165 returns all boxes, both spent and unspent, so it's not suitable for checking the number of unspent boxes.

Since the fragmentation check is not critical, I decided to turn it off for now until a proper way to check the number of unspent boxes is implemented on ergo-graphql or other backend.