user-config, user defaults lib, make -> meson, astyle -> clang-format, led states, other bugfixes

[carlossless]

• [x] replace make usage with meson (hopefully allows better configuration of modular source)
• [x] replace style with clang-format (also ran from meson)
• [x] first version of keyboard and layout dir hierarchy
• [x] receiving and saving led states (as part of keyboard state)
• [x] a few bug fixes regarding key report sending (but many more to go, and some fixes are still hacks)

Overall there are still many things to fix, clean up and implement...