Phase field homogenisation

[gervilquin]

With the approval of this pull request, I ensure that I have completed the following points:

• [ ] I have run the AllTests.m file and all the tests have passed successfully.
• [ ] I have run the AllTutorials.m file and no error was obtained in the command window. Note: don't forget to discard the .msh, .res and .vtu files obtained from this stage.
• [ ] I have written my code following the morphology and relevance rules defined in: https://github.com/SwanLab/Swan/wiki/Clean-code-rules.
• [ ] Any new file created from scratch is located inside the most appropriate folder, taking into account the code topic.