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.
Simplifies examples of embedding a certificate file or a root cert.
This is a much cruder mechanism than the full flash filesystem we want
eventually, but still sometimes useful.
