Added H1 norm to Error filter

Issue/feature addressed

The FilterError does output L2- and Linf-norm, but no H1 norm which is sometimes required for comparison against literature.

Proposed solution

Since the H1 norm is already defined on a ExpList/MultiRegions level. We just have to add the H1 norm to the FilterError call.

Implementation

Add H1Error interface to EquationSystem and add it to the FilterError::Update routine. The H1 error is then written to file for each variable.

Tests

• None

Suggested reviewers

Jacques Xing

Notes

Checklist

• Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).