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.
* contact 3d patch test, standard lagrange, small sliding, linear tet4 elements
* tet4 dual basis contact patch test pass
* contact 3d patch test, standard lagrange, small sliding, linear tet4 elements
* tet4 dual basis contact patch test pass
* Patch test for linear elements standard lagrange / dual lagrange pass now
* Patch test for quadratic contact surfaces for standard + dual basis pass
* refactoring
* renamed files
* Improvements to preprocess scripts
* convert several elements to node sets in one command
* possibility to find particular node from mesh filtered by node set
* 2d small sliding contact patch test, linear elements
* Added backward compatibility
* 2d contact algorithms pass patch tests
* test data for 2d contacts
* no common models in different tests. testing generalized alpha stabilization
* Preprocess tests
* moved tests from test_preprocess_aster_reader.jl to test_preprocess.jl
* generalized-alpha time integration, alpha=0.0 by default
* Improvements to logging
* JuliaFEM.jl: can set environment variable to one of logging levels: OFF, CRITICAL, ERROR, WARNING, INFO, DEBUG
* problems_contact_2d_autodiff.jl: do not loop over nodes if logging level != DEBUG
Jukka Aho