profiles: fix application

moving to a DB meant empty slices in the Configuration & Policy structs
were being stored as null, and striking a nerve with Jellyfin.
Mediabrowser library change fixed that by de-nulling them itself, and a
new bool field called "Homescreen" is now used to decide if a profile
has a homescreen layout stored or not. This field is hopefully correctly
filled in during migration.

models.go

@@ -25,6 +25,7 @@ type newUserDTO struct {
 	MatrixContact   bool   `json:"matrix_contact"`                              // Whether or not to use matrix for notifications/pwrs
 	CaptchaID       string `json:"captcha_id"`                                  // Captcha ID (if enabled)
 	CaptchaText     string `json:"captcha_text"`                                // Captcha text (if enabled)
+	Profile         string `json:"profile"`                                     // Profile (for admins only)
 }
 
 type newUserResponse struct {