build+lncli: default to hex encoding for byte slices

This commit swaps out golang/protobuf/jsonpb for a custom variant that
by default prints byte slices as hex, which is more useful for our
setting. Some existing wrapper structs are removed as they can now be
printed directly with the new jsonpb.

!!! NOTE !!!

This commit introduces a breaking change to lncli listinvoices since
payment hashes and preimages will now be printed in hex instead of
base64.

go.sum

@@ -134,6 +134,8 @@ github.com/lightninglabs/neutrino v0.11.0 h1:lPpYFCtsfJX2W5zI4pWycPmbbBdr7zU+Baf
 github.com/lightninglabs/neutrino v0.11.0/go.mod h1:CuhF0iuzg9Sp2HO6ZgXgayviFTn1QHdSTJlMncK80wg=
 github.com/lightningnetwork/lightning-onion v0.0.0-20191214001659-f34e9dc1651d h1:U50MHOOeL6gR3Ee/l0eMvZMpmRo+ydzmlQuIruCyCsA=
 github.com/lightningnetwork/lightning-onion v0.0.0-20191214001659-f34e9dc1651d/go.mod h1:rigfi6Af/KqsF7Za0hOgcyq2PNH4AN70AaMRxcJkff4=
+github.com/lightninglabs/protobuf-hex-display v1.3.3-0.20191212020323-b444784ce75d h1:QWD/5MPnaZfUVP7P8wLa4M8Td2DI7XXHXt2vhVtUgGI=
+github.com/lightninglabs/protobuf-hex-display v1.3.3-0.20191212020323-b444784ce75d/go.mod h1:KDb67YMzoh4eudnzClmvs2FbiLG9vxISmLApUkCa4uI=
 github.com/ltcsuite/ltcd v0.0.0-20190101042124-f37f8bf35796 h1:sjOGyegMIhvgfq5oaue6Td+hxZuf3tDC8lAPrFldqFw=
 github.com/ltcsuite/ltcd v0.0.0-20190101042124-f37f8bf35796/go.mod h1:3p7ZTf9V1sNPI5H8P3NkTFF4LuwMdPl2DodF60qAKqY=
 github.com/ltcsuite/ltcutil v0.0.0-20181217130922-17f3b04680b6/go.mod h1:8Vg/LTOO0KYa/vlHWJ6XZAevPQThGH5sufO0Hrou/lA=