Fix #8048

Fixes #2012

Fix #7559

Fix #7559

Fix issue #7166

Remove gravatar and no-avatar functionality, prepare for default avatars even more and reword some stuff

 - Use camelCase

 - Add some phpdoc

 - Fix some indents

 - Use some more spacing

doesn't work anymore, because now the datetime is saved as string (ref #2975)

we get best results regarding mime type detection if we use fileinfo - let's tell the admin about that

Currently it only allows the admin to enable or disable the HTTPS
enforcement, but in the future it could be expanded to further options.

The HTTPS enforcement only allows the admin to enforce it, if he is
connected via HTTPS. (To prevent admins to enable it without a proper
SSL setup)

add a check and a warning if the ownClodu server is not able to establish http connections to the internet. The reason is that users complained that external filesystem support, the update checker, downloading of new apps or the nowledgebase don´t work and don´t know why.