Add support for visualizing prolly tree and blob messages in `dolt show`

[nicktobey]

This PR does a couple things:

1. dolt show #address can now display the internals of a ProllyTreeMap message (typically used for storing indexes). Previously, only splunk/noms show could do this.
2. Both dolt show and splunk can now display the contents of a Blob message.
3. If a ProllyTreeMap leaf node contains a value that is itself an address (example: the value of text and json columns), that value is shown as a human readable address, which can be fed back into dolt show or splunk to explore the whole tree.

[coffeegoddd]

@nicktobey DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
01806a8	ok	5937457

version	total_tests
01806a8	5937457

correctness_percentage
100.0

[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
0cfade0	ok	5937457

version	total_tests
0cfade0	5937457

correctness_percentage
100.0

[nicktobey]

Yeah, specific hashes in the tests does seem like it could be brittle. I guess the better solution would be to dynamically get the hashes during the test. But that would require calling and parsing dolt show several times starting with the commit hash, and that seemed like a hassle.

If this turns out to be brittle, I'll take responsibility for improving the tests. But for now I think this is fine.