Create Speaker module for Admin

[luciagirasoles]

Implement the Speakers module in the admin panel.

• Updates Speaker model
• Generate Speaker controller for the html response
• Add the routes for index, show, new, edit, update. (In order to handle association when a speaker is already in a record speaker_event, destroy has to be managed in a different issue)
• Update navbar and errors to be managed by bootstrap styles and events.
• Add HTTParty to verify urls for social media links.

Desktop View:

Mobile:

Close #179