Merging master into eosio_build_symbol

Remove Ricardian contracts

Fedora: moved directory opt/boost_1_67_0 to opt/boost

Fix unable to delegatebw when the receiver has cast his stake

Disallow net_plugin empty messages; guard peeking at varint

increase default leeway to 3 ms

Fix message_buffer peek; make peek & read throw on error

OOB block signing

Merging master into eosio_build_fedora

Add two hardening checks on initial message parsing in net_plugin:

Don't accept messages that indicate a length of 0 -- we would need at least the net_message's variant "what" varint to have a useful message.

Stop peeking at a net_message's what varint after 5 bytes; anything more is invalid.

This commit fixes two problems with message_buffer. First, users of read() (like fc::raw::unpack) expect that on an out of bounds read that read() throws. You can see this behavior in fc::datastream where its read() will throw an out_of_range_exception. The boolean returned from fc:: datastream::read() is always true. So for both message_buffer read() and peak() throw an out_of_range_exception when attempting to read or peak beyond the end. peak() is something that is only used internally to net_plugin and it appears that net_plugin expects it to throw too as all uses of it don't check for its return value.

The second fix is that peak()'s logic for detecting end of buffer didn't seem right. It always based the number of bytes remaining on the read index no matter where we are peaking from. So that needed fixing too.

 - address PR feedback

Create missing system RCs

Merging master into eosio_build_fedora

Build Centos: moved opt/boost_1_67_0 to opt/boost

Build Ubuntu: moved opt/boost_1_67_0 to opt/boost

 - fix program option description and default

change default max-irreversible-block-age to unlimited

Added test for rejected duplicate transfer

 - consolidate http(s) parameters and http_client management in a new http_client_plugin for any appbase-based app

json parsing fixes #3539