Option to open lists vertically (#1381)

* Add configuration option to open lists vertically

* Add tests, clean up vertical list config

* Vertical list option cleanup

* Use is# for tests
* Order properties in documentation alphabetically

test/test_ale_info.vader

@@ -66,6 +66,7 @@ Before:
   \  'let g:ale_linters = {}',
   \  'let g:ale_linters_explicit = 0',
   \  'let g:ale_list_window_size = 10',
+  \  'let g:ale_list_vertical = 0',
   \  'let g:ale_loclist_msg_format = ''%code: %%s''',
   \  'let g:ale_max_buffer_history_size = 20',
   \  'let g:ale_max_signs = -1',