Moved slicing for long titles to model

[#67574168]
Added styles for buttons

- Adjusted color of PDF button

- Referenced new Font Awesome icon
Added Open Graph meta tags

[#76531236]

Added og tags to individual book page
Merge branch 'develop' of https://github.com/emory-libraries/readux into develop

Conflicts:
readux/books/templates/books/snippets/volume_header.html
readux/books/templates/books/snippets/volume_links.html
Merge branch 'develop' of https://github.com/emory-libraries/readux into develop

Conflicts:
	readux/books/templates/books/snippets/volume_header.html
	readux/books/templates/books/snippets/volume_links.html