Add icons in tabs:

• the plus icon, when add a new page
• the stylus icon for edit page
• the eye icon, when preview a page

Additional task:

When tab viewType changes, in 6.1 the icon did not change, which is undesirable. 

Steps to reproduce in 6.1:

1. If DEMO is still 6.1.x, open https://demo.magnolia-cms.com/.magnolia/admincentral#app:pages:detail;/travel/tour-type:edit otherwise open a local instance travel tour-type page in edit mode.
2. Notice stylus icon
3. Press preview action button.
4. Notice stylus icon (should be eye)
5. Optionally, do the same, but start with preview (eye icon) and switch to edit mode (eye icon stays)

When implementing the subapp icons, refresh the icon with viewType change. (backport probably unnecessary)