Tooling cleanup and manifest reorganization

[puddly]

The commits describe the changes but I'll summarize them here:

• Passing --build-dir is no longer required, a semi-unique one will be created under build/ in the current directory.
• CMake support has been removed, as SLC-CLI does not generate functional CMake projects at the moment.
• Derive the root project path in a stable way, allowing for manifests to be relocated.
• Move all Nabu Casa manifests under manifests/nabucasa
• Remove --device from the Simplicity Commander CLI. We did not compute it correctly and it is not needed for any firmware we generate.
• Spawn the SLC daemon in CLI mode for a massive speed boost:

  Version	Time
  Old	28s
  New	20s
  New (--keep-slc-daemon, second run)	7s

• Use just slc instead of slc-cli on all platforms.

CC @tube0013