add Download logfile button to admin settings

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