Commits or PRs that do not respect the clang-format style that we
enforce will fail the test.
Adding ubuntu-toolchain-r-test as its libstdc++ is necessary to install
libllvm-3.9.
- `certs` and `editor_fonts` go to `thirdparty`
- `dist` and `scripts` go to a new `misc` folder
- `collada` and `doc` go to `tools/editor`
The next step will be to rename `tools/editor` to `editor` directly,
but this will be done at the right time to avoid breaking too many PRs.
