Bugfix: move the assignments before the return statements

Old code:

     if (delete_state == 'delete_button_1_clicked') {
         return false;
         delete_state = 'confirmation_needed';
     } else if (delete_state == 'delete_button_cancel_clicked') {
         return false;
         delete_state = 'basic';

New code:

     if (delete_state == 'delete_button_1_clicked') {
         delete_state = 'confirmation_needed';
         return false;
     } else if (delete_state == 'delete_button_cancel_clicked') {
         delete_state = 'basic';
         return false;
Rename strengthener methods

Double       -> Double last due time interval
Proportional -> Double last actual time interval
Add translations to new features
Update help with new features
Remove "relearn old words" word order

Probably it does not work in practice. If we need something for relearning old
words, a more complex algorithm has to be created.
Update release notes
Remove garbage
Document hidden features
Implement HTML dictionaries and custom CSS

- Add `text_format` and `css` fields to WDict
- Parse HTML words in two ways (unmodified HTML vs adding <br>s)
- Add custom CSS to HTML when editing/practicing/searching words
- Add translation
- Add help
Practice page: Add full screen mode
Update Release Notes
TODO updated
Document import formats
Version set to 0.14.0