Fix error notice

This is a minor release, with a single bugfix:

• Fix error caused by improperly checking the chosen CSP mode when outputting headers (thanks @reatlat).

UI improvements and more directives

• Improved UI, with CSP directives divided into collapsible categories.
• Add all remaining non-deprecated CSP directives.
• Warn if enabling upgrade-insecure-requests on a site that does not support HTTPS.
• Sanitize directives on save and disallow newlines in header content.
• Various internal improvements.

Some additional CSP directives

This is a relatively small update, that only contains a few more CSP directives. The next update will contain even more, along with an updated user interface.

• Add some commonly used CSP headers that were missing (thanks Master Dan).
• Add some other user requested directives.
• Fix some translator comments.

First version

• Support for different policies for admin, logged-in frontend and regular visitors.
• Different policies can have different reporting/enforcing mode.
• Directives can be configured separately, to easier see what is allowed in which cases.
• Support for configuring the Report-To header.