Move WebException stack trace from User error to verbose log

[HebaruSan]

Problem

Download errors look like this currently:

Continue? [Y/n] 

Downloading "https://spacedock.info/mod/1805/Whirligig%20World/download/0.10.0"
System.Net.WebException: The remote server returned an error: (404) NOT FOUND.
  at System.Net.HttpWebRequest.GetResponseFromData (System.Net.WebResponseStream stream, System.Threading.CancellationToken cancellationToken) [0x00146] in <88f564ea69dd4dc8ba9bf979e48d5996>:0 
  at System.Net.HttpWebRequest.RunWithTimeoutWorker[T] (System.Threading.Tasks.Task`1[TResult] workerTask, System.Int32 timeout, System.Action abort, System.Func`1[TResult] aborted, System.Threading.CancellationTokenSource cts) [0x000f8] in <88f564ea69dd4dc8ba9bf979e48d5996>:0 
  at System.Net.HttpWebRequest.EndGetResponse (System.IAsyncResult asyncResult) [0x00020] in <88f564ea69dd4dc8ba9bf979e48d5996>:0 
  at System.Net.WebClient.GetWebResponse (System.Net.WebRequest request, System.IAsyncResult result) [0x00000] in <88f564ea69dd4dc8ba9bf979e48d5996>:0 
  at System.Net.WebClient.GetWebResponseTaskAsync (System.Net.WebRequest request) [0x0008d] in <88f564ea69dd4dc8ba9bf979e48d5996>:0 
  at System.Net.WebClient.DownloadBitsAsync (System.Net.WebRequest request, System.IO.Stream writeStream, System.ComponentModel.AsyncOperation asyncOp, System.Action`3[T1,T2,T3] completionDelegate) [0x0008d] in <88f564ea69dd4dc8ba9bf979e48d5996>:0 
One or more downloads were unsuccessful:

Error downloading WhirligigWorld 0.10.0: The remote server returned an error: (404) NOT FOUND.

This is scary-looking and redundant; the WebException stack trace does not contain useful information, and we summarize all the errors at the end after that anyway.

All UIs are affected in the same way.

Cause

When an error happens, this line tells NetAsyncModulesDownloader:

CKAN/Core/Net/NetAsyncDownloader.cs

Line 433 in 5b08975

onOneCompleted.Invoke(downloads[index].target.url, downloads[index].path, downloads[index].error);

... which then prints the exception with User.RaiseError.

Changes

Now we put that stack trace into log.Info instead, so it won't be visible by default but you can re-enable it with --verbose.

Continue? [Y/n] 

Downloading "https://spacedock.info/mod/1805/Whirligig%20World/download/0.10.0"
One or more downloads were unsuccessful:

Error downloading WhirligigWorld 0.10.0: The remote server returned an error: (404) NOT FOUND.