Make versions tab non-interactive inside install flow

[HebaruSan]

Problem

The Versions tab is available on the recommendations screen, but the checkboxes don't do anything, and the stability override dropdown throws an exception:

System.InvalidOperationException: This BackgroundWorker is currently busy and cannot run multiple tasks concurrently.
   at System.ComponentModel.BackgroundWorker.RunWorkerAsync(Object argument)
   at CKAN.GUI.Main.RefreshModList(Boolean allowAutoUpdate, Dictionary`2 oldModules)
   at CKAN.GUI.Main.StabilityToleranceConfig_Changed(String identifier, Nullable`1 relStat)
   at CKAN.Configuration.StabilityToleranceConfig.SetModStabilityTolerance(String identifier, Nullable`1 relStat)
   at CKAN.GUI.Versions.StabilityToleranceComboBox_SelectionChanged(Object sender, EventArgs e)
   at System.Windows.Forms.ComboBox.OnSelectionChangeCommitted(EventArgs e)
   at System.Windows.Forms.ComboBox.OnSelectionChangeCommittedInternal(EventArgs e)
   at System.Windows.Forms.ComboBox.WmReflectCommand(Message& m)
   at System.Windows.Forms.ComboBox.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

Cause

These interactive UI elements are only available because the rest of mod info is potentially useful in evaluating recommended mods to install. The dropdown needs to force an update of the mod list (in case changing it makes some mods newly installable or uninstallable), which requires using the progress screen, which is already doing something else while the install flow is active.

Changes

Now the Versions tab's checkboxes and dropdown are hidden on the recommendations screen.

Fixes #4290.