LibGUI+Applications: Default the SpinBox min/max to the full int range

By default, a SpinBox's value should be unlimited, (or as close as we
can get to that,) and then the GML or code can impose a limit if
needed. This saves the developer from entering an arbitrary "big" max
value when they want the value to have no maximum.

I've audited the use of SpinBox and added `min: 0`, and removed a `max`,
where appropriate. All existing SpinBoxes constructed in code have a
range set explicitly as far as I can tell.

Userland/Applications/Calendar/AddEventDialog.gml

@@ -120,7 +120,6 @@
             name: "duration_hour"
             fixed_size: [50, 20]
             min: 0
-            max: 999999
         }
 
         @GUI::SpinBox {

Userland/Applications/FontEditor/FontEditorWindow.gml

@@ -35,6 +35,7 @@
                 @GUI::SpinBox {
                     name: "glyph_editor_width_spinbox"
                     preferred_width: "fit"
+                    min: 0
                 }
 
                 @GUI::CheckBox {

Userland/Libraries/LibGUI/FontPickerDialog.gml

@@ -48,6 +48,7 @@
 
             @GUI::SpinBox {
                 name: "size_spin_box"
+                min: 0
             }
 
             @GUI::ListView {

Userland/Libraries/LibGUI/SpinBox.h

@@ -42,8 +42,8 @@ class SpinBox : public Widget {
     RefPtr<Button> m_increment_button;
     RefPtr<Button> m_decrement_button;
 
-    int m_min { 0 };
-    int m_max { 100 };
+    int m_min { NumericLimits<int>::min() };
+    int m_max { NumericLimits<int>::max() };
     int m_value { 0 };
 };