IF: Add more extensive tests for finalizer voting behavior

[greg7mdp]

Resolves #2233.

This PR adds some unit test for finalizer voting that validate correct checks for monotony, liveness and safety.

It also adds to stream output functions for some types used by the finalizer, which allows to use these types in BOOST_ASSERT_EQUAL macros which provide better output when they fail than BOOST_ASSERT.

It also adds spaceship operator comparisons to some fc types (including sha256) and block_timestamp, which allows to define default spaceship comparison operators in new types containing these (as is the case for block_ref).

[ericpassmore]

Note:start
group: IF
category: TEST
summary: Adds unit test for finalizer voting that validate correct checks for monotony, liveness and safety. Adds support for adds spaceship operator comparisons to some fc types, and support for BOOST_ASSERT_EQUAL to some types used by finalizer.
Note:end