Show clicked issue data in the sidebar

app/assets/javascripts/boards/components/board_card.js.es6

...assets/javascripts/boards/components/board_sidebar.js.es6

app/assets/javascripts/boards/models/issue.js.es6

app/assets/javascripts/boards/models/milestone.js.es6

app/assets/javascripts/boards/stores/boards_store.js.es6

app/assets/javascripts/right_sidebar.js

app/controllers/projects/boards/issues_controller.rb

app/views/projects/boards/components/_sidebar.html.haml

...ws/projects/boards/components/sidebar/_assignee.html.haml

...ws/projects/boards/components/sidebar/_due_date.html.haml

...iews/projects/boards/components/sidebar/_labels.html.haml

...s/projects/boards/components/sidebar/_milestone.html.haml

...ojects/boards/components/sidebar/_notifications.html.haml