This change allows AppFramework applications to specify a custom CSP header for example when the default policy is too strict. Furthermore this allows us to partially migrate away from CSS and allowed eval() in our JavaScript components.
Legacy ownCloud components will still use the previous policy. Application developers can use this as following in their controllers:
```php
$response = new TemplateResponse('activity', 'list', []);
$cspHelper = new ContentSecurityPolicyHelper();
$cspHelper->addAllowedScriptDomain('www.owncloud.org');
$response->addHeader('Content-Security-Policy', $cspHelper->getPolicy());
return $response;
```
Fixes https://github.com/owncloud/core/issues/11857 which is a pre-requisite for https://github.com/owncloud/core/issues/13458 and https://github.com/owncloud/core/issues/11925
*Changes:*
* "… is not yet properly setup" in line 24 is changed to " … is not yet set up properly" (better word order and space in the middle of "set up", as it is a participle of the verb "to set up").
* "internet" is corrected to "Internet" with a capitalized "I" in lines 54 and 59.
* Also in line 54: "3rd party" is changed to "third-party" to for a more coherent spelling across the different ownCloud components.
* "… apps don´t work" is corrected to "… apps won't work" (with a proper (and hopefully correctly escaped) (apostrophe)[http://en.wikipedia.org/wiki/Apostrophe#Typographic_form] instead of the (acute accent)[http://en.wikipedia.org/wiki/Acute_accent]).
* Still in line 54: The negation is corrected from "… might also not work" to "… might not work, either".
This enforces proper types on POST and GET arguments where I considered it sensible. I didn't update some as I don't know what kind of values they would support 🙈
Fixes https://github.com/owncloud/core/issues/14196 for core
Some code paths called the `normalizePath` functionality with types other than a string which resulted in unexpected behaviour.
Thus the function is now manually casting the type to a string and I corrected the usage in list.php as well.