nm-applet: disable auto-refresh and return the option of the manual refresh button

 * Cinnamon version (cinnamon --version)
Cinnamon 5.2.7

 * Distribution - (Mint 17.2, Arch, Fedora 25, etc...)
NAME="Linux Mint"
VERSION="20.3 (Una)"

 * Graphics hardware *and* driver used
Device-1: Intel driver: i915 v: kernel 

 * 32 or 64 bit
x86_64

Issue
The panel is positioned at the top.

When I click on the nm-applet icon, a menu appears. Then, after doing absolutely nothing for several seconds, it refreshes the available wifi APs' list, expanding the menu vertically. As a result, all buttons lower to the APs' list moves down (how far - depends on how many new APs have been discovered).

As a result, if I want to open up an nm-applet menu and open network settings, more often than not the network settings button will shift down before I manage to click on it. As a result, my click will hit some other button: either a preconfigured VPN connection (and I'll unintendedly be connecting to VPN) or some wifi AP (and I'll disconnect from my current wifi AP and start connecting to my neighbour's wifi)

Steps to reproduce

1. move cinnamon panel from the bottom of the screen to the top
2. be surrounded by plenty of visible wifi APs
3. be connected to one of the wifi APs
4. do not open nm-applet for several minutes (so that the cached wifi AP entries would be evicted from the nm-applet list)
5. reasonably quickly click on the nm-applet, move your cursor to the "Network Settings" option
6. do not move the mouse. The APs' list will refresh and push the "Network Settings" button down. Now your mouse cursor is on some other option in the list, most likely - some newly discovered wifi AP.

Should you have clicked swiftly on the "Network Settings", you would've most likely have actually hit something else but the intended button.

Expected behaviour
a) There is an option in nm-applet's settings to toggle between automatic APs' refresh (like it is now) and manual APs' refresh using a "refresh" button (like it used to be a few Cinnamon versions ago)
b) (less UX-friendly): prefetch the APs' list when nm-applet is clicked on and render it when the nm-applet opens (will make the UI more sluggish)
c) the available APs' list has 1 fixed position, by default showing the current WIFi connection. When proactively clicked on, it expands down/up and shows other available connections (either lazy or eager fetched). Adding a scrollbar when there are too many entries would eliminate the need for the "more >" option at the bottom of the list.

Start at the nm-applet menu and its available-AP refresh behavior, then reproduce the panel-at-top scenario with cached entries being refreshed after opening. Compare the proposed automatic, manual-refresh, and prefetch behaviors and determine which interaction is intended. Done should prevent the menu controls from shifting unexpectedly, while providing the requested manual refresh option if that approach is selected.