Setup up menus when the theme is installed.
Delete the nav menus when removing the theme.
Create the nav menu after the theme's installed, not on page load.

Also, we should no longer have a static 'Profile' link.

**Fixes #99.** Previously, we were creating the nav menu in the database
on every page load :scream:. That broke because when no one is logged
in, they don't have permissions to create the menu.
Append the profile link to the nav menu.
Merge branch 'feature/after_switch_theme' into develop
Merge branch 'develop' of github.com:scholarslab/ivanhoe into develop