Channel handshake ChanOpenInit improvements

[colin-axner]

Summary

Apply spec changes. These changes have already been done for ChanOpenTry. These changes should be broken into smaller pieces if multiple parts of core IBC need to be modified. Please see the workflow I did for #640 for inspiration.

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[colin-axner]

I think this is probably fine to do in one function since #640 help set the groundwork for these changes

Suggested ways of maybe breaking down the pr:

• modify OnChanOpenInit API to return version string, pass version into WriteChannelState
• ics20 - add a check if the version passed in is empty, if so return the ics20 version
• ics27 - no code should be changed, the version passed must be non empty since it indicates specific connection choices (as well as tx and encoding type)
• ics29 - if no version is specified it should not enable fees and pass onto underlying app
• add a field to MsgChannelOpenInitResponse to return the selected version (probably should be done for MsgChannelOpenTry as well)

The general idea of the spec changes is that OnChanOpenInit now returns a version. If the passed in version is non empty, it should perform legacy logic (validate the version, if err != nil, return error else return version). If the passed in version is empty, the application may choose to select a default version (if possible) otherwise return error