HumHub v1.18.0-beta.4 release notes

Enh #7690: Allow uploading a custom Email Header image, or using the Logo image
Fix #7690: Remove “Mobile appearance” from Appearance form
Fix #7697: Fix submitting a form with file upload from a modal window
Fix #7699: Fixed old Mailer Vars usage
Fix #7700: styling


Fix #7701: Activity Box Bottom Padding
Fix #7702: Selectors/Pickers BG color
Fix #7554: Delete logging DB table (keep log only)
Fix #7704: Maintenance mode alert box
Enh #7620: Add box shadow to cards (such as cards in the People and Spaces pages)
Enh #6969: Added UserHelper for better user param method handling
Enh #7695: Extend permissions for group manager
Enh #7703: New ActiveFileUpload field widget
Enh #7716: Use Altcha captcha provider by default instead of Yii captcha, and upgrade Altcha library to v1.1
Fix #7715: Enable Bootstrap box-shadows, mainly for dropdown menus