Enhance filesystem.process_file get_metadata cache performance. (#353)

Reduce exiftool calls by using a metadata object cache. 
Enable single exiftool subprocess to elimate spawing exiftool for each image.

elodie/filesystem.py

@@ -543,7 +543,7 @@ def process_file(self, _file, destination, media, **kwargs):
         directory_name = self.get_folder_path(metadata)
         dest_directory = os.path.join(destination, directory_name)
         file_name = self.get_file_name(metadata)
-        dest_path = os.path.join(dest_directory, file_name)
+        dest_path = os.path.join(dest_directory, file_name)        
 
         media.set_original_name()
 
@@ -589,7 +589,7 @@ def process_file(self, _file, destination, media, **kwargs):
             #  before we made any changes.
             # Then set the utime on the destination file based on metadata.
             os.utime(_file, (stat_info_original.st_atime, stat_info_original.st_mtime))
-            self.set_utime_from_metadata(media.get_metadata(), dest_path)
+            self.set_utime_from_metadata(metadata, dest_path)
 
         db = Db()
         db.add_hash(checksum, dest_path)
@@ -642,4 +642,4 @@ def should_exclude(self, path, regex_list=set(), needs_compiled=False):
                 compiled_list.append(re.compile(regex))
             regex_list = compiled_list
 
-        return any(regex.search(path) for regex in regex_list)
+        return any(regex.search(path) for regex in regex_list)