Move 2bcontact.cc to newly created directory 'src'

'src' is where Dune modules are expected to have these files.

CHANGELOG.md

+Changes in dune-contact v2.6.0
+==============================
+
+* There is now a subdirectory `src`, and some of the compilable source code
+  files have moved there.  This makes `dune-contact` more consistent with
+  other Dune modules.
+
 Changes in dune-contact v2.5.0
 ==============================
 

CMakeLists.txt

@@ -13,13 +13,11 @@ dune_project()
 
 add_subdirectory(doc)
 add_subdirectory(dune)
+add_subdirectory(src)
 add_subdirectory(test)
 dune_symlink_to_source_files(FILES resources)
 
 set(programs "")
-if(HAVE_AMIRAMESH)
-  list(APPEND programs 2bcontact)
-endif()
 if(HAVE_AMIRAMESH AND HAVE_IPOPT)
   list(APPEND programs 1badaptmeasure 1bcontact het2bcontact 2bnonlincontact 2bmgnonlincontact)
 endif()

src/CMakeLists.txt

+set(programs "")
+#if(HAVE_AMIRAMESH)
+  list(APPEND programs 2bcontact)
+#endif()
+
+foreach(_program ${programs})
+  add_executable(${_program} ${_program}.cc)
+  target_link_dune_default_libraries(${_program})
+  add_dune_amiramesh_flags(${_program})
+  add_dune_ipopt_flags(${_program})
+  add_dune_ug_flags(${_program})
+  add_dune_psurface_flags(${_program})
+  add_dune_mpi_flags(${_program})
+  target_compile_options(${_program} PRIVATE "-fpermissive")
+endforeach()
+