Fix powerline-lint tests

Some notes on the commit:

1. As there are no plugin-local themes present in powerline/config_files 
   corresponding keys were removed from local_themes dictionary.
   Note that these theme names are incorrect since they contain slash.
2. As external_ip and email_imap_alert segments seem to be removed corresponding 
   segment_data keys also were removed.
3. Various files that import vim module now have the usual workaround that sets 
   vim local to dummy object on error.
4. Syntastic check was failing because it did not specify which highlighting 
   groups it uses in documentation. I made it specify them and also moved format 
   strings to keywords.
5. powerline-lint script got --debug argument. Pretty useless currently though: 
   it only makes it output traceback for ImportError when failing to import 
   module to stderr.