Run TRSP update in its own thread

[csete]

Currently the TRSP update function runs in the main GUI thread and this can cause the GUI to freeze. TRSP update should run in its own thread and report progress and status through appropriate channels.

[csete]

Alternatively, we could use async calls in GIO.

[gvanem]

Since we now use WinInet API for remote files on Windows, this can be done using a callback set in InternetSetStatusCallback() and calling InternetOpen (..., INTERNET_FLAG_ASYNC). Ref:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa385096(v=vs.85).aspx

[csete]

We need to look at GIO. The module needs a complete rewrite anyway.