Optional plugins build

Now possible to build only required plugins and skip all others.
Also can get fail if required plugins can't be built.
By default will be build all possible plugins.

New cmake cache variables:

ENABLE_PLUGINS - list plugins to build (botan;ossl;gnupg for example).
                 Also possible values is none, auto or all
                 (by default: "auto")

WITH_${PLUGIN}_PLUGIN - to build particular plugin. Can be no, yes or
                        auto (WITH_ossl_PLUGIN=auto for example)