Replace the optional argument `no-install` by a global variable named
`spacemacs-sync-packages`.
Rename the hooks to reflect the renaming of the function.
Rename the flag `--no-sync` to the more explicit `--no-package-sync`
More advanced timing of functions and loading with
--debug-init --adv-timers [N]. The last arg is optional and specifies
the threshold time for placing entries in the *load-timers* buffer.
1. Make sure debug-on-error stays on
2. Force verbose loading
3. Detect long requires and loads (with --timed-requires)
4. Start profiler (with --profile)
