Fix wallet unit tests

[xandronus]

Fixes #210

A couple of different issues with these tests:

1. LiteDB has some rounding behaviour for datetime's which if you are using LiteDB for a wallet you should be aware of. This was causing tests to fail.
2. There was a couple of tests that used test data that made assumption of date/time locality. I corrected those to be explicit.

[dangershony]

But wallet unit tests are not failing are they?

[dangershony]

I assume this will fix the linux failures