Add link to create new link in link widget
Add a web interface for most settings

- Those settings had to be moved to the database.
- A table layout version number is added to the database. Will be used
in the future for easy updating.
- Added a new page system, which allows pages to execute code before the
page output has started.
Move page specific logic out of Website constructor

Also fixes website title being set before pages have a chance to edit
them.
Move login screen over to new page system

Prevents additional page reloads