Add isChannelActive method

[shuse2]

Expected behavior

add isChannelActive method in order to check if the partner chain is active or not. This is necessary to check if the cross chain transaction is possible or not in the verify step of a command.
The specification is defined in this PR

Actual behavior

Without this method, it is not possible to check the state of the channel from other module

Steps to reproduce

N/A

Which version(s) does this affect? (Environment, OS, etc...)

6.0.0-beta.2-