Move torrent edit and upload into 'torrents' blueprint

Move supporting functions and variables into other files
* nyaa.views.torrents:
  - _create_upload_category_choices
* nyaa.backend:
  - get_category_id_map

nyaa/backend.py

@@ -12,6 +12,19 @@ from orderedset import OrderedSet
 from ipaddress import ip_address
 
 
+@utils.cached_function
+def get_category_id_map():
+    ''' Reads database for categories and turns them into a dict with
+        ids as keys and name list as the value, ala
+        {'1_0': ['Anime'], '1_2': ['Anime', 'English-translated'], ...} '''
+    cat_id_map = {}
+    for main_cat in models.MainCategory.query:
+        cat_id_map[main_cat.id_as_string] = [main_cat.name]
+        for sub_cat in main_cat.sub_categories:
+            cat_id_map[sub_cat.id_as_string] = [main_cat.name, sub_cat.name]
+    return cat_id_map
+
+
 def _replace_utf8_values(dict_or_list):
     ''' Will replace 'property' with 'property.utf-8' and remove latter if it exists.
         Thanks, bitcomet! :/ '''