Subspace should be a hash value

[kwunyeung]

subspace in Post is better in hash value so that it can be verified by the users by comparing the hash value instead of relying on comparing with a string.

Consider an imposter is trying to build an app and put subspace as C0SMOS to pretend to be an app discussing things on COSMOS.

But I don't have an idea of how the UX can be done to let normal endusers to verify this yet. @RiccardoM @bragaz please comment.

[RiccardoM]

I'm personally in favor of this change. This would just require one small additional check inside the Validate method of both MsgCreatePost and Post types:

• susbspace should be a valid SHA-256 hash in HEX form

This can be easily done using the following RegEX:

^[a-fA-F0-9]{65}$

[leobragaz]

This makes sense, also because with only strings we can have users writing "deSmOs", "desm0s" and so on..We will provide a better order using hash so I totally agree with implementing this.

[kwunyeung]

I have one comment in the PR #84 (comment)