Create 02 client spec in v2 core folder

[AdityaSripal]

Create the 02 client spec for v2 folder

• Remove delay period passing in
• Specify the register counterparty message and handler

[sangier]

In ICS20 we decided to:

• create a v1 folder
• move the original spec into the v1 folder
• update the original readme with the V2 version.

For confirmation, are we going to use the same approach here or, for now and until we have a clear restructure repo plan, we prefer to create v2 folders and place there the new spec versions?