Fixes#146
Can be optionally activated by the FlatPress admin
* Content Security Policy is an effective measure to protect your site from XSS attacks. By whitelisting sources for approved content, you can prevent the browser from loading malicious content.
* Permissions Policy is a new header that allows a site to control which features and APIs can be used in the browser.
* HTTP Strict Transport Security is an excellent feature to support on your site and strengthens your implementation of TLS by getting the User Agent to enforce the use of HTTPS.
* The X-Download-Options response header instructs the browser not to open the file directly but to offer it for download first. This mitigates some potential Social Engineering attacks.
* HTTP Strict Transport Security (HSTS for short) is a security mechanism for HTTPS connections that protects against both connection encryption downgrade attack and session hijacking.
* The referrer policy directive determines whether, and if so which, referrer information for requests triggered by the current web page is sent by the web browser in HTTP requests.
Fixes#201 and #144
* In the admin area of the style Flatmaas-Rev is no longer tried via stylesheet to include the image nib-logo.png.
* In the preview of the Leggero style "Posted by + time" is now displayed right-aligned - as in the blog.
* The heading for posts and pages has received its own CSS class "entry-title".
* In all three styles, both heading sizes are now displayed correctly; as in the blog, so in the preview.
* The publication date is truncated from h2 and now uses h6.
* Font size h4 can now also be conveniently set via BBCode button.
* Long single line code in leggero-v2 style is now wrapped when printing.
This closes issue #197
Please check if it works with php8.1. Tested with php 7.4
Update main.php
'el-gr','es-es','fr-fr' removed as browser language, because the FlatPress setup currently has no language files for it
Update lang.de-de.php
Update main.php
some code formatting
