External links should not always open in a new window

Problem/Motivation

Opening external links in a new window is not always preferable. It would be good to have an option to determine how to handle external links

Steps to reproduce

1. Add an external link
2. Note the external icon
3. Note that the link opens in a new window

Proposed resolution

1. Add a theme option to toggle whether links should open in a new window.

Remaining tasks

1. Create a utility function for getting the base link variables that every link uses. Currently this should be link text, url, is_external, is_new_window
2. Within this utility function we use theme options to determine whether to open the link in a new window.

User interface changes

API changes

Data model changes