Add Components table to database

[seesarahcode]

• Create Components table
• Add publication_id column - integer
• Add title column - string
• Add subtitle column - string
• Add comp_type column - string
• Add due_date column - datetime
• Add validation for publication_id column (presence)
• In Publications table add: has_many :components
• Components table should: belongs_to :publication
• Create factories
• Write passing unit tests
• Create seed data