Improve policy capability support in policy toolchain

[stephensmalley]

Introduce warnings in the policy compiler toolchain for inconsistent combinations of policy capabilities and policy rules, e.g. using classes/permissions in rules without enabling the corresponding policy capability and vice versa.
Investigate lighter weight policy capability support, so that we can introduce new policy capabilities without needing to patch libsepol each time just to enable/use the new capability, e.g. allow passing capabilities to the kernel via uninterpreted string name rather than bitmap.