feat: talks index page

[jonathanrib3]

Problem

Closes Issue #571 - Tasks index page

Solution

To add the index page i created a controller to Talk model and created the view. The page's styled is based on /contributions page so it follows the same structure, but with pagination and without the 'go to top page' button at the bottom of the page.

This feature has feature tests too on /spec/feaetures/index_talks_spec.rb

When the current user doesn't have saved talks

When the current user does have saved talks

[carloslopes]

Seria importante também testar o caso onde o usuário acessar a lista de talks e não consegue visualizar talks de outros usuários