User tags

[andersoncardoso]

• Add tags abstraction to user
• tags use an postgres array column
• the Tag model is used for indexing and fulltext search (for autocompletion). Use through the Taggable concern
• Taggable adds .searchable_tags method to index any array column
• Add tags input component
• Simplify js loading to use single file (no more controller specific loading)
• Add pg_search to use fulltext search with postgresql
• Update docs on tagging and search