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
add logSettingsController
add download logfile button
move getEntries to LogSettingsController
move set log level to logsettingscontroller.php
add warning if logfile is bigger than 100MB
add unit test for set log level
fix typecasting, add new line at EoF
show log and logfile download only if log_type is set to owncloud
add unit test for getFilenameForDownload
