Miner safety

The miner previously was not safely handling alterations to the consensus database. Now, if there are problems, instead of refusing to start the miner will correctly perform a rescan. Startup time will be a lot slower, but at least the program will start at all.

I wanted to make this the best PR possible, but unfortunately that resulted in me needing to implement several new features. Test coverage is still not 100% for this PR because I don't think it's the appropriate time or place to start mocking filesystems, but other than dependency mocking to trigger errors, this PR has full coverage.