Use sqlite to store seeds / proofs / etc

[ethanfrey]

Replace attempt at adding two indexes using the file system (seeds by height and hash), with a standard system. Seems nicer to use sqlite than leveldb:

• for the interactive client and easy for inspection
• for the tooling including migration frameworks
• for powerful query possibilities

performance is not much of an issue as long as db is not too big (<<1 GB ???) maybe more if the binary data is stored separately, and that limit is more about meta-data. should not be major issue for clients.

[ethanfrey]

Info on sqlite

Max db size seems to be several gb: https://softwareengineering.stackexchange.com/questions/332069/what-is-a-realistic-real-world-maximum-size-for-a-sqlite-database

Seems they support decently powerful secondary indexes https://sqlite.org/lang_createindex.html

Performance storing large blobs : https://sqlite.org/intern-v-extern-blob.html

[ethanfrey]

Moved to basecoin repo, as the cli type stuff is all there.