Make ignores configurable

Adds config file setting PAPERLESS_CONSUMER_IGNORE_PATTERNS.

paperless.conf.example

@@ -57,6 +57,7 @@
 #PAPERLESS_CONSUMER_POLLING=10
 #PAPERLESS_CONSUMER_DELETE_DUPLICATES=false
 #PAPERLESS_CONSUMER_RECURSIVE=false
+#PAPERLESS_CONSUMER_IGNORE_PATTERNS=[".DS_STORE/*", "._*", ".stfolder/*"]
 #PAPERLESS_CONSUMER_SUBDIRS_AS_TAGS=false
 #PAPERLESS_OPTIMIZE_THUMBNAILS=true
 #PAPERLESS_POST_CONSUME_SCRIPT=/path/to/an/arbitrary/script.sh