Move the current posts constants to chain parameters

[RiccardoM]

Context

Currently when checking the validity of the posts when the user creates or edited one, there are the current checks that are performed:

• a post cannot be over 500 character long
• the maximum number of optional fields is 10
• each optional field value can be at most 200 characters long

While all these values have currently worked out pretty good, having them hard coded creates two main problems:

1. in order to know their value you need to check at the chain code;
2. they are arbitrarily chosen by us and cannot be changed without a source code edit.

Solution

In order to solve both above mentioned problems, I think we should move them from being hard-coded inside the keys.go file to be on-chain parameters. This would allow:

1. everyone to query those specifications (particularly useful for clients);
2. changeable through governance proposals.

In order to do this we can do the same way that other modules do it. A reference can for example be the x/gov module of the Cosmos SDK. The references files should be (might not be a complete list):

• keeper/params.go
• types/params.go

Also the params registration should be done inside the app.go file as well (app.go registration for the gov params).