* Refactor post_list to have a wrapper for calling
    respective posts
  * Use unread API for loading posts on load.
  * Use since or before_id based on the channel status
    of posts.
  * Clear postInChannel when entering from a view which is not at
    latest post
  * Take a backup before clearing posts as we might need it incase of
    network issues.
  * Always use oldest postId or newest postId for loading posts.
  * Fix async render of channelView by using a flag on channelView.
  * Change dependency of post_list to have channeId instead of channel.
  * Add channel selector for channel_intro_message component.
  * Add constants for AFTER_ID and BEFORE_ID.