[WIP] Deep freeze - Githubissues

High Level Overview of Change

This PR implements Deep Freeze feature described in this specification: XLS-77d

Added new flags and functionality allowing trust lines to be deep-frozen.

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] Refactor (non-breaking change that only restructures code)
[ ] Performance (increase or change in throughput and/or latency)
[x] Tests (you added tests for code that already exists, or your new feature included in this PR)
[ ] Documentation update
[ ] Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
[ ] Release

[x] Public API: New feature (new methods and/or new fields)
[ ] Public API: Breaking change (in general, breaking changes should only impact the next api_version)
[ ] libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
[ ] Peer protocol change (must be backward compatible or bump the peer protocol version)