Fix for errors editing/uploading books with duplicate tags/authors/language names

Additional parsing of epubs for cover files
Fix for change of database with linked read_column and read column isn't present any more

cps/helper.py

@@ -468,6 +468,14 @@ def generate_random_password():
     passlen = 8
     return "".join(s[c % len(s)] for c in os.urandom(passlen))
 
+
+def uniq(input):
+  output = []
+  for x in input:
+    if x not in output:
+      output.append(x)
+  return output
+
 ################################## External interface