refactor: refactor migrations and add fixtures

feat: introduce key-value store
feat: imprint page (resolve #23)
chore: remove default user
chore: remove packr

models/shared.go

@@ -1,6 +1,16 @@
 package models
 
+import "github.com/jinzhu/gorm"
+
 const (
 	UserKey       = "user"
+	ImprintKey    = "imprint"
 	AuthCookieKey = "wakapi_auth"
 )
+
+type MigrationFunc func(db *gorm.DB) error
+
+type KeyStringValue struct {
+	Key   string `gorm:"primary_key"`
+	Value string
+}