Required at project level because some components use header files in
other components' submodules, and one component with a
submodule (esptool.py) doesn't have or need a component.mk.
New makefile component_wrapper.mk allows some variables to be set
before component.mk is evaluated. This properly fixes problems with
sdkconfig being hard to access in all phases of the build.
Including component_common.mk is no longer necessary and will print a
deprecation warning for components which use it.
Reduces number of make invocations, allows variables exported in project
to be seen in all component make processes, not just the main ones.
Also makes a no-op build about 3x faster than it was.
Angus Gratton