Update Essentials restart behavior

This is about what should happen after Essentials was restarted (after a rebuild). Details are TBD, but in general this covers:

• should the "rebuilding" dialogue get updated to state that Essentials is available again?
• where do you go from there? Always "Installed Features"? Where, when and how do we indicate what new things are available now?
• can we restart the application and jump to a specific location?

What will be done on completion of this task:
remove "close" button, so you can't close the dialogue.
dialog closes implicitly by rebooting the essentials application.

Drop the current "homepage", the UX design doesn't have one.
When starting up, go directly to
1) the introduction page when the global parameters haven't been set yet - done
2) the Installed features page if there is at least one installed feature
3) the Library otherwise