Update test pagination

Fixes the test so that it expands the date range before trying the
search. This increases the likelihood it has > 50 messages which it
requires to do the test. If it doesn't, then it fails with a helpful
error message.

Fixes #148
Fix is_newer_messages_link_visible test to be faster

Switch to use is_newer_messages_link_not_visible which doesn't have an
implicit wait and is thus a lot faster to execute in good conditions.
Merge pull request #164 from willkg/update-test-pagination

Update test pagination