Use clang-tidy.

[thorstenhater]

Allow (opt-in) to run clang-tidy on Arbor.

Limitations currently are:

• excluded
  • lmorpho
  • modcc
  • tests (clang-tidy doesn't always see EXPECT_EQ(a, b) as a use of a and b)
• exclude all dependency by --- rather crudely --- dropping a .clang-tidy into the src-dirs
• only the default set of checks is in use clang-analyzer-*
  • more / advanced checks are added as a comment in .clang-tidy but require fixing more issues.
  • modernize: useful, but at least in one instance dangerously wrong std::vector<size_t>(size, val) => {size, val}
  • misc: has some interesting things, especially wrt included headers, but it's a lot of noise.
  • bugprone: use after free, while important, has some issues.

Sensible suggestions were implemented and as only two
weird ones remained, I massaged the code to appease the
Linter despite being quite sure of a false positive.

Things left disabled can be toggled on after a while.

[boeschf]

cscs-ci run default