Fix when the list of updates is auto-refreshed

[ParticleMon]

Is your feature request related to a problem? Please describe.

1. Automatically refreshing the list of updates when opening mintupdate can be between undesirable and counterproductive; for instance, when one's objective is to change a preference, manage kernels, or see if mintupdate has an update (due to Icon not shown when an update is available to mintupdate #932), and not to actually check for updates.

2. The list of updates is auto-refreshed when returning from Edit > Preferences and Edit > Software Sources.

Describe the solution you'd like
In Preferences > Auto-refresh:

1. Make the first option something like "Refresh the list of updates at program launch"
2. Revise "Refresh the list of updates automatically" to "Refresh the list of updates automatically in the background"
3. Do not auto-refresh updates when returning from Preferences or Software Sources.