add has many tags through relationship with taggings to user and bookmark model
before saving tag make name lowercase
use alternative method of lowercasing name for Tag model
add index to name column on tags table
add an accessor tag_list for easier use of tags
sideload tags and tagging relationship in  bookmarks controller
sideload taggings and tags relationship
include tags and taggings ids in json representation
override json representation
override json representation
include ids of tags and taggings within json representation of user