Move riak_core.proto from riak_core.

This protobuff definition is only used by KV. Whether we should
continue to use this encoding can be debated separately, but putting
the file in KV removes yet another dependency from Core. Third parties
who use Core can pull in protobuffs via riak_api or their own
applications. For KV, it is pulled as a dependency of riak_api.

/cc @Vagabond @evanmcc @jrwest
Add max/warn object size & sibling thresholds

Reading or writing objects whose binary representation is bigger than
warn_object_size will generate a warning in the logs identifying the
bucket/key and size for the object.

Putting an object whose binary size is greater than max_object_size will
fail.

We will now warn if writing more than warn_siblings and fail to put if
more than max_siblings.
Adjust routes and add helper functions for bucket types.
Whitespace cleanup.
Add bucket types support to riak_kv_wm_buckets.
Add bucket type support to riak_kv_wm_props.
Add support for bucket types to riak_kv_wm_object.

* Changed explicit bucket type to use api_version = 3, unset/default
  uses 2.
* Left links alone but this could cause confusion later. PB already
  disallows bucket-types in links.
* Added another arity to riak_kv_wm_utils:format_uri to handle the
  inclusion of bucket types when generating the URI.
Go ahead and move maybe_bucket_type/2.
Add bucket types support to riak_kv_wm_keylist.
Add recognition of bucket types in riak_kv_wm_link_walker.

The original bucket-types proposal suggested that links and
link-walking would not be handled. This keeps consistency with that
proposal, returning 403 on link-walking requests scoped to a bucket
type other than the default.
Add support for bucket types to riak_kv_wm_index.
Fix typo.
Fix some more bugs in resources around bucket types.
Fix bucket name bug in wm_props.

Also use atom_to_binary/2 instead of l2b/a2l combo.
Add resource for bucket-type properties.
Fixed call to undefined function in kv_mutator
Add support for bucket types in JSON mapred.
Re-add 1.4 counter code. Make counters in 2.0 backwards compatible
Update v1 counter for v2 API
Add a no-op inc/dec by zero to pncounter

Update test to use legacy mod
@TODO add tests for othe mods/generalize kv_crdt_eqc