Limit the length of posts

[RiccardoM]

Context

As discussed inside #61, we should limit the length of posts to 500 characters. Longer should be uploaded to IPFS in order to avoid an uncontrolled grow of the chain on-disk size.

Solution

The solution is pretty straightforward and can be implemented as a check inside the MsgCreatePost, MsgEditPost and Post#Validate methods:

if len(post.Message) > 500 {
  // return error
}