Notify user when a command execution error occurs (#171)

With this PR, whenever command execution fails, the user will get an
error message with details of the error that can be passed on to
developers

An unrelated minor change: errors caused by task cancellations will no
longer be logged

---------

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>
Signed-off-by: mctaylors <mctaylxrs@outlook.com>

src/Messages.Designer.cs

@@ -996,5 +996,21 @@ namespace Octobot {
                 return ResourceManager.GetString("MessagesClearedFiltered", resourceCulture);
             }
         }
+
+        internal static string CommandExecutionFailed
+        {
+            get
+            {
+                return ResourceManager.GetString("CommandExecutionFailed", resourceCulture);
+            }
+        }
+
+        internal static string ContactDevelopers
+        {
+            get
+            {
+                return ResourceManager.GetString("ContactDevelopers", resourceCulture);
+            }
+        }
     }
 }