Simplify Reactable scopes API

[antonkomarev]

Resolves #93

[antonkomarev]

@JFunu changed virtual columns prefix from reactions_ to {$type}_ in PR #97 and this PR changes it to more standardized reaction_{$type}_ to follow the same style with total counters prefix reaction_total_.

Article::query()
    ->joinReactionCounterOfType('Like')
    ->joinReactionCounterOfType('Dislike')
    ->joinReactionTotal()

It will produce attributes:

• $article->reaction_like_count
• $article->reaction_like_weight
• $article->reaction_dislike_count
• $article->reaction_dislike_weight
• $article->reaction_total_count
• $article->reaction_total_weight