A combination of using isset() instead of count() or strlen(), caching the
chunkify function, and replacing is_numeric() with some comparisons

When `mod_unique_id` is enabled the ID generated by it will be used for logging. This allows for correlation of the Apache logs and the ownCloud logs.

Testplan:

- [ ] When `mod_unique_id` is enabled the request ID equals the one generated by `mod_unique_id`.
- [ ] When `mod_unique_id` is not available the request ID is a 20 character long random string
- [ ] The generated Id is stable over the lifespan of one request

Changeset looks a little bit larger since I had to adjust every unit test using the HTTP\Request class for proper DI.

Fixes https://github.com/owncloud/core/issues/13366

This reverts commit 96a93192.

for password protected link shares the password is stored in shareWith, so we need to set this manually to null for the hooks

The URL was previously encoded twice which leads to getting redirected to a 404 page when the password has been entered incorrect at least once.

Testplan:

- [ ] Opening `http://localhost/core/index.php?redirect_url=%2Fcore%2Findex.php%2Fsettings%2Fadmin` redirects to the admin page when providing the correct credentials
- [ ] Opening `http://localhost/core/index.php?redirect_url=%2Fcore%2Findex.php%2Fsettings%2Fadmin` redirects to the admin page when providing the invalid credentials and then providing valid ones.
- [ ] Logging in as admin then going to the admin page and clearing the cookies and refreshing will show the login and when repeating the above test steps you're redirected correctly.

Fixes https://github.com/owncloud/core/issues/9804

Since the Storage interface isn't ready to work directly with exceptions
like Forbidden and NotFound, the DAV storage has been adapted to still
return false when expected.

Fixes https://github.com/owncloud/core/issues/13657

Can happen when trying to instantiate external storages that have
incomplete config, where the constructor throws an exception (the
exception is caught in createStorage())

IAppManager lives in OCP\App and not in OCP.

Fixes https://github.com/owncloud/core/issues/13710

disable the app code checker - some previous shipped apps cannot be installed from the appstore now :facepunch:

There might be the case that `fopen($file, 'r')` returns false and thus ownCloud might believe that the config file is empty and thus potentially leading to an overwrite of the config file.

This changeset introduces `file_exists` again which was used in ownCloud 5 where no such problems where reported and should not be affected by such problems.

Ref https://github.com/owncloud/core/issues/12785#issuecomment-71548720

Ref https://github.com/owncloud/core/issues/13693#issuecomment-71546767

certificate manager should always use a \OC\Files\View otherwise we will get problems for different primary storages