DAWN-487 ⁃ Update Chainbase to Support Scoping

[bytemaster]

Currently chainbase makes some assumptions that are not valid for EOS.IO:

• the set of tables is static
• undo / redo applies to all tables which is not sustainable

Going forward we will require the following:

• scoped tables
• dynamic table creation
• scoped undo history
  • dynamic addition of tables as they are modified

After reviewing the design of chainbase I have concluded the following usage pattern will be necessary going forward:

• all create, modify, and remove commands must be triggered from the undo session
  • this is done to ensure that the impacted tables have the proper revision history, current
    implementation can skip this because ALL tables have undo started at same time, but going
    forward this will have to be sparse.
• all child undo sessions must be created from the current undo session
• in debugging mode we need to ensure that all access to create/modify/remove is through a single strand

When the last irreversible block comes along we discard old / unneeded undo states via the commit() call. We currently iterate over all tables (which are statically typed) and delete unnecessary undo state. This won't be possible going forward unless we include the undo sessions in the shared memory.

[andriantolie]

@bytemaster is this still relevant?

[brianjohnson5972]

@wanderingbort or @heifner This looks like this is OBE because it was written so many designs ago. If I hear nothing back from you I will close it.

[brianjohnson5972]

Code has been refactored multiple times since this was written, so it is OBE