layer.conf: Update to use mickledore as the layer series name

layer.conf: Update to use mickledore as the layer series name

OE-Core has changes which do need careful evaluation for compatibilty,
such as the addpylib directive. Move the core later names to mickledore
so layers can mark their compatibility as such.

Also increase the version number for core. If we do make further changes
that need layer changes, we'll update the version again so layers can mark
compatibility within the series.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>