Update to use modern CMake practices, tighten warning levels

[mosra]

Various good-to-have things to do:

• [ ] replace include_directories() with target_include_directories(), preferring PRIVATE where possible; if a dependency provides a CMake target use that instead
• [x] remove use of file(GLOB), list sources explicitly (makes the build more predictable without things getting broken when there are untracked files in the working copy) -- #158
• [x] use configure_file() instead of add_definitions() -- #143
• [x] convert if(${FOO}) to just if(FOO) -- #58
• [ ] look into TODOs with CMAKE_CXX_VISIBILITY_PRESET
• [x] ~~set up some JOB_POOLS so it's possible to use more cores for compilation without risking OOM issues (currently a compilation of one pybind11 file takes up to 1.8 GB of RAM, we definitely don't want to run that together with 7 other jobs)~~ will not be needed after #64 lands, since it reduces the bindings code quite a lot
• [ ] enable CORRADE_USE_PEDANTIC_FLAGS for all Habitat code (postponed from #116)
• [x] ~~go back to CMake 3.5 since that's the oldest version currently in widespread use (Ubuntu 16.04)? -- blocked by tinyply, which requires 3.10 (#139) (which is blocked by magnum's mesh import rework)~~ no need to be that backwards compatible
• [ ] look into suppressing warnings from dependencies
  • [x] glog has some (or go with #121 instead)
  • [ ] assimp needs -fvisibility-inlines-hidden to fix ld: warning: direct access in function 'Assimp::IOSystem::CurrentDirectory() const' from file 'deps/magnum-plugins/src/MagnumPlugins/AssimpImporter/libAssimpImporter.a(AssimpImporter.cpp.o)' to global weak symbol 'Assimp::IOSystem::CurrentDirectory() const::Dummy' from file 'deps/assimp/code/libassimp.a(Importer.cpp.o)' means the weak symbol cannot be overri dden at runtime. This was likely caused by different translation units being compiled with different visibility settings.

[Skylion007]

@mosra Can this be closed?

[mosra]

Why? There's still a few good-to-have items from the list that are not done yet. Feel free to tackle those, if you have time.

[aclegg3]

@mosra any more updates here?

[mosra]

Hmm. Do we have any other place to list such low-priority tech debt TODOs? In my case (with Magnum repos) I have a bunch of such long-lived "aggregate issues" full of checkboxes that act more as a reminder of what needs to be eventually solved, and I opened this one with a similar intent.

But if the aim here is to only have an issue open if it's likely to be resolved soon, feel free to close.

[aclegg3]

I'll leave this open for now until we establish such a list and then we can migrate the remainder there.