start work on #112

get decryption working
temp checkin
Continue to address #112

Clean up a lot of bugs with the key-puller class and different corner cases.
better error message for tracking failure
Fix a bug introduced in v0.0.26 with tracking and proof generation after key revocation.

We still need to hold onto the last link

Also, add keypull in more places we might need it, like tracking.
Merge branch 'issue_112'

Conflicts:
	CHANGELOG.md
	lib/sigchain.js
	src/sigchain.iced