Add page settings, improve settings UI

CHDataManagement/Model/Settings/PageSettings.swift

@@ -0,0 +1,17 @@
+import Foundation
+
+final class PageSettings: ObservableObject {
+
+    /// The prefix of the urls for all pages
+    /// The full path will be `<pagePrefix>/<page-url-component>`
+    @Published
+    var pageUrlPrefix: String
+
+    @Published
+    var contentWidth: Int
+
+    init(pageUrlPrefix: String, contentWidth: Int) {
+        self.pageUrlPrefix = pageUrlPrefix
+        self.contentWidth = contentWidth
+    }
+}