Update theme settings

- When I add new options specific to a theme the default theme settings look disorganized without labels. Specifically added "Theme Content" as the last section. Extra fields added may belong in this section and can be done by leaving the `label` empty. 
- Removed "(shown in sidebar)" that was on the about text label. It is often not found in the sidebar.
- Removed login and credit options. These options are most often not used.