This changes the "ipfs swarm limit" command so that When limit changes
are applied via the command line, they are persisted to the repo
config, so that they remain in effect when the daemon restarts.

This also removes limit.json support, to simplify the behavior. The
schema for Swarm.ResourceMgr.Limits is exactly the same as limit.json,
so existing limit.json can be dropped into the IPFS config easily
using something like:

cat ~/.ipfs/config | jq ".Swarm.ResourceMgr.Limits = $(cat limit.json)" | sponge ~/.ipfs/config

This upgrades to Resource Manager v0.3.0, which exports the config
schema so that we don't have to maintain our own copy of it.

Makes sure we evaluate the config JSON directly, so we catch any
regressions around serialization too.