Tidy-up of Collection library

Issue/feature addressed

This is a tidy-up of the Collection library.

Proposed solution

Implementation

• Use default keyword for destructors
• Move factory at the beginning of the file
• Use pCollExp[0]->GetShapeDimension() when appropriate
• Consistently use pCollExp[0]->GetTotPoints()
• Remove unused code

Tests

Suggested reviewers

Please suggest any people who would be appropriate to review your code.

Notes

Please add any other information that could be useful for reviewers.

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).