ENH: adjust user preset handling

1. async fetch user presets from server (in thread)
2. always load default user presets
3. load user presets from cache immediately
4. not remove user presets cache
5. hide some loading ui

Change-Id: I1d29ed18e09606d0b2f69a69eea2eb5042c26223

src/slic3r/GUI/Widgets/ProgressDialog.cpp

@@ -608,6 +608,8 @@ bool ProgressDialog::Pulse(const wxString &newmsg, bool *skip)
     return m_state != Canceled;
 }
 
+bool ProgressDialog::WasCanceled() const { return m_state == Canceled; }
+
 bool ProgressDialog::DoBeforeUpdate(bool *skip)
 {
     // we have to yield because not only we want to update the display but