Adding STL support and changing volume check to relative test

[jhcollins]

Mandatory Checklist

Please ensure that the following criteria are met:

• Title of pull request describes the changes/features
• Request at least 2 reviewers
• If new files are being added, the files are no larger than 100kB. Post the file sizes.
• Code coverage did not decrease. If this is a bug fix, a test should cover that bug fix. If a new feature is added, a test should be made to cover that feature.
• New features have appropriate documentation strings (readable by sphinx)
• Contributor has read and agreed with CONTRIBUTING.md and has added themselves to CONTRIBUTORS.md

As a general rule of thumb, try to follow PEP8 guidelines.

Description

Adding support for using setting up STL boundary conditions
changing lumped mass matrix/volume check to relative test.