Adding ability to fetch posts around a specifc post

store/store.go

@@ -86,6 +86,8 @@ type PostStore interface {
 	Get(id string) StoreChannel
 	Delete(postId string, time int64) StoreChannel
 	GetPosts(channelId string, offset int, limit int) StoreChannel
+	GetPostsBefore(channelId string, postId string, numPosts int, offset int) StoreChannel
+	GetPostsAfter(channelId string, postId string, numPosts int, offset int) StoreChannel
 	GetPostsSince(channelId string, time int64) StoreChannel
 	GetEtag(channelId string) StoreChannel
 	Search(teamId string, userId string, params *model.SearchParams) StoreChannel