Generalize PostReaction

[bedeho]

Currently, we have

pub enum PostReaction {
    /// No any reaction
    NonReacton,

    /// Thumb up to a post
    ThumbUp,

    /// Thumb down to a post
    ThumbDown,

    /// Like a post
    Like,
}

Now, if anyone wanted to replace the application-level semantics of either variant to something else, such as Like to Hate, then they would either have to accept a naming conflict with the runtime or fork the module. More importantly, if they wanted to increase the number of reaction types, they would have to fork the module. We can treat this a bit more generally by just having the reaction encoded as some integer like type, and accept the number of different reactions accepted as a trait configuration for the module. This would allow for forkless customization without any penalty in clarity of performance.

[bedeho]

Done.