Refactor looking up SIG reference details into a common location, taking it out of the individual spot providers. This means we can now look up references properly from Cluster spot comments, etc. Closes #74 as there is no longer any duplication of these lookups. Works towards #54 as sig_refs now specify their sig internally.

alertproviders/wota.py

@@ -54,9 +54,7 @@ class WOTA(HTTPAlertProvider):
                           dx_calls=[dx_call],
                           freqs_modes=freqs_modes,
                           comment=comment,
-                          sig="WOTA",
-                          sig_refs=[SIGRef(id=ref, name=ref_name, url="https://www.wota.org.uk/MM_" + ref)] if ref else [],
-                          icon=get_icon_for_sig("WOTA"),
+                          sig_refs=[SIGRef(id=ref, sig="WOTA", name=ref_name)] if ref else [],
                           start_time=time.timestamp())
 
             # Add to our list.