* 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.
Moved plane contact related stuff to own separate package
`MortarContact2D.jl`, where the development continues.
The following changes to test files are done:
1) Problem name for plane mortar coupling is `Mortar2D` (was `Mortar`
before), and later on 3d coupling will be `Mortar`. So the dimension
of coupling operator is explicitly given in a problem name.
2) Before elements to coupling was defined using
```julia
update!(problem.elements, "master elements", master_elements)
add_elements!(problem, [slave_elements; master_elements])
```
Now, explicitly give master and slave elements as
```julia
add_slave_elements!(problem, slave_elements)
add_master_elements!(problem, master_elements)
```
Keep on mind that Lagrange multipliers are in slave side.
Jukka Aho