to a "constants" class

Fixed the quota storage wrapper to correctly return the quota value when
the free space is not known (which usually happens when the disk_free_space
function is disabled)

This will make oC create previews for MKVs.

Test file: http://www.auby.no/files/video_tests/h264_720p_hp_5.1_3mbps_vorbis_styled_and_unstyled_subs_suzumiya.mkv

To test this just apply this change and upload the test file, if an preview is generated this change is most likely working as expecting.

Moved the mounting code for external storage from
OC\Filesystem::initMountPoint to files_external using the
post_initMountPoints hook

introduce reopen() method to be used for unit test execution only - right after a unit test has been executed the session will be reopened

Instead of leave two decimal places which is confusing, round the byte
values correctly to the closest byte.

In environments where the data folder is mount from another partition,
it is important to check that the data folder we see is actually the
real one. If the mount failed for some reasons, this fix will make
ownCloud temporarily unavailable instead of causing unpredictable
behavior.

If trusted_domains is not set after a CLI upgrade, show a warning in the
output.