Extra Stat collection (#407)

* Cleaned up error interceptor to avoid sending auth errors (when a 500 occurs) to sentry as auth errors aren't issues.

* Added extra stat collection

* Fixed a bad gitignore which ignored anything in a stats directory

API/DTOs/Stats/UsageInfoDto.cs

@@ -0,0 +1,24 @@
+using System.Collections.Generic;
+using API.Entities.Enums;
+
+namespace API.DTOs.Stats
+{
+    public class UsageInfoDto
+    {
+        public UsageInfoDto()
+        {
+            FileTypes = new HashSet<string>();
+            LibraryTypesCreated = new HashSet<LibInfo>();
+        }
+
+        public int UsersCount { get; set; }
+        public IEnumerable<string> FileTypes { get; set; }
+        public IEnumerable<LibInfo> LibraryTypesCreated { get; set; }
+    }
+
+    public class LibInfo
+    {
+        public LibraryType Type { get; set; }
+        public int Count { get; set; }
+    }
+}