Set up different .htaccess files

- Add two new .htaccess files; one for dev, and one for prod.
- Remove the original .htaccess file from git tracking
- Modify the .gitignore file appropriately.
NOTE: This change requires a manual creation of a hard link on the
server. From the public_html/wp-content/uploads folder, run “ln
.htaccess_dev .htaccess,” or the prod one, as appropriate.