Allow using "/" in "overwritewebroot"

Whenever the reverse proxy is using "/" as the webroot, it is now
possible to set that value in "overwritewebroot"
always encrypt files to owner
there is no need to re-calculate the shares after a touch
Correctly read the full stream in file_get_contents

When using user-defined stream wrappers, PHP will
return a maximum of 8192 bytes even if more was
requested.

This fix uses stream_get_contents to make sure the full stream is read
and not only the first 8 KB.

Added unit test with a bigger test file to cover this case.
Added missing fclose in file_get_contents and file_put_contents
fix h3 style, move out from settings to apps CSS
Merge pull request #7979 from owncloud/core-fixfilegetcontentsloop

Correctly read the full stream in file_get_contents
Upgraded phpseclib to version 0.3.6
Fix admin-dir_permissions redirection when cannot write warning
is shown.
Merge pull request #7968 from owncloud/core-overwritewebrootwithroot

Allow using "/" in "overwritewebroot"
Merge pull request #7977 from owncloud/fix_enc_if_sharing_is_disabled

always encrypt files to owner
Merge pull request #8006 from wakeup/master

Fix admin-dir_permissions redirection when cannot write warning is shown.
Merge pull request #8003 from owncloud/extstorage-sftp-upgradephpseclib

Upgraded phpseclib to version 0.3.6 (SFTP ext storage)
Merge pull request #7995 from owncloud/fix-h3-styles

fix h3 style, move out from settings to apps CSS
Reuse known free space in the files app
Merge pull request #7978 from owncloud/enc_cleanup

there is no need to re-calculate the shares after a touch
Merge pull request #8014 from owncloud/uploadsize-reuse

Reuse known free space in the files app
[tx-robot] updated from transifex
Add option to getUsersSharingFile() to get the paths for the shared users