[Satellite] Quick fix to latency issue

Run web request for TLEs on a background
thread in order to avoid stalling the UI.
This fixes the worst symptoms of
nasa/MCT-Plugins#94 (the unresponsive UI)
but does not address usability concerns.
Merge pull request #95 from VWoeltjen/mctPlugins94q

[Satellite] Quick fix to latency issue