Feat: Change umask of homedir to 077

[dorianim]

This changes the umask of userhomes to 077 (Permissions will be 700 respectively) to prevent other users from accessing their data. The default is 022 which makes it possible for users to access other users data if they know the explicit path.
See:

• http://linux-pam.org/Linux-PAM-html/sag-pam_mkhomedir.html
• https://ask.linuxmuster.net/t/linuxclient-verzeichnisrechte/8607

@kiarn @PLanB2008 do you see any unwanted implications of this?

[codeclimate]

Code Climate has analyzed commit 4687547 and detected 0 issues on this pull request.

View more on Code Climate.

[kiarn]

Hello,

It's surely a good point, but we must test it and wait on feedback from test users.
Teachers can access the students data via shares, so this change should not have bad consequences.
I will also test it in my environment.

Arnaud