Don't use aux_source_directory in new CMake projects

When creating a new CMake project, the list of sources gets defined in CMakeLists.txt as

aux_source_directory(. SRC_LIST)

However, this is bad practice, because CMake cannot notice when new files are added to the project until it is explicity re-run. Cf. https://cmake.org/cmake/help/v3.6/command/aux_source_directory.html

Instead, Creator should use explicitly set SRC_LIST, maybe leaving room for adding more files:

set(SRC_LIST
  newly_created_file.c
)