* Fix deprecation warnings from tests
* Refactor tests so that ´@testset` is usually called in master file
`runtests.jl`, not inside test file. Later on we can convert tests
to examples.
* Syntax of tests now follow more closely syntax used currently in
JuliaFEM. We have had earlier studies with different kind of syntaxes,
now we have kind of explicit way to do things.
Heat transfer analysis is moved to its own package where the development continues. Two small modifications are needed for test files:
- Instead of `problem.properties.formulation`, we have two separate problems, `PlaneHeat` for two-dimensional problems and `Heat` for three-dimensional problems.
- Unnecessary prefixing of field names is changed. For example, now we simply have only "thermal conductivity" and not prefixed "temperature thermal conductivity".