Clean up unclear/unneeded code.

Removed:
- one unused "then" template from step definitions;
- "not of good type" type checking.

Changed:
- steps starting with "I should have received kanjis" will now assert
  result to not be empty;
- various beautifications.
Added radical_id feature.

Radical ID is now read from kanjidic files, and can be used as a
filter to search for kanjis.