add export genesis tests

[colin-axner]

Summary

we need tests which ensure that all the genesis fields are exported and that the exported genesis is valid

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[fedekunze]

have you considered using the new in-store migrations instead?

[colin-axner]

have you considered using the new in-store migrations instead?

yup! Already implemented that in #205. Unfortunately we should keep genesis upgrades around as a backup solution. As it stands, it isn't possible to change the chain id just via an x/upgrade since tendermint loads the chain id from the gen doc and doesn't expose a way to change it block to block

Supporting genesis upgrades is a lot of work and the process is clumsy at best, but if for some reason something goes wrong with x/upgrade or a chain id must be incremented, it is nice knowing there's always a backup option available