Add and improve tests

Some unit tests are already present :

• For C++ applications based on ctest : 51 tests with test/ directory and tests on applications.
• For python_src based on pytest (in python_TSX branch, for now) : with complete runs of two use cases and test on subchain (with mocks)

In order to improve coverage, several tests must be added :

• For C++ applications :

  • Add tests for TSX products : SARDeramp
  • Use git-lfs to avoid test dependancies (see #15)

• For python_src:

  • Tests on TSX processing
    • from internal_processings package
      • resamping
      • filtering
    • for each subchain by mocking internal processing)
  • Tests for PostProcessing chain
  • Tests on ConfigFile class