Thumbnail Generation Refactoring (#16)

* Fix file_list and convert save_first_frame to use FFMPEG directly

* All thumbnail generation now uses FFMPEG engine

lib/workers/base_worker.py

@@ -5,7 +5,6 @@ import os
 import subprocess
 import threading
 import json
-import glob
 from datetime import datetime
 from enum import Enum
 
@@ -287,7 +286,7 @@ class BaseRenderWorker(Base):
 
     def file_list(self):
         job_dir = os.path.dirname(self.output_path)
-        file_list = glob.glob(os.path.join(job_dir, '*'))
+        file_list = [os.path.join(job_dir, file) for file in os.listdir(job_dir)]
         file_list.sort()
         return file_list