Move server-version comparers to own script

[smurthys]

The commits in this PR make the following changes:

• Move functions that compare server-versions to their own script
• Move unit tests for server-version comparers to their own script
• Add the new script to db-core installer

This change is being done in preparation for server-version specific code as part of Milestone 4 (M4).

Fixes #255

[smurthys]

Thanks for the reviews.