Merge #11651: refactor: Make all #includes relative to project root (laanwj, MeshColl...

Merge #11651: refactor: Make all #includes relative to project root (laanwj, MeshCollider, ryanofsky)

7b91b5f Remove trailing whitespace causing travis failure (MeshCollider)
434f5a2 Recommend #include<> syntax in developer notes (Russell Yanofsky)
96b9281 refactor: Include obj/build.h instead of build.h (Wladimir J. van der Laan)
138016b test: refactor: Use absolute include paths for test data files (Wladimir J. van der Laan)
e7b3163 qt: refactor: Changes to make include paths absolute (Wladimir J. van der Laan)
0c71521 build: Remove -I for everything but project root (Wladimir J. van der Laan)
5b56ec9 qt: refactor: Use absolute include paths in .ui files (Wladimir J. van der Laan)
1a44534 scripted-diff: Replace #include "" with #include <> (ryanofsky) (MeshCollider)

Pull request description:

  Rebase of #11053

  Previously started by @laanwj, ACK'ed by promag, ryanofsky, jonasschnelli, and concept-ACK'ed by practicalswift and jnewbery. Thus should be almost RTM :)

Tree-SHA512: d8d25248309deb06a54686c4a6bafd290ba69dcd0df391a50d1caed2c22ff2659be442459bdd9d1fc3b6a1360ba0804a907b1402d206df3e1cb6e8924e3c7f3e