Fixed autogeneration of the new code for the task.
Created Subtheme class as active record based model.
Implemented relation between Theme and Subtheme classes. Prepared initial data for subthemes.
Implemented additional dropdown for available subthemes for the selected theme.
Created migration adding subtheme_id column to tasks table. Implemented relationship between Subtheme and Task classes.
Implemented filtering for selected theme and subtheme.
Added the column and form field displaying the task subtheme.
Improved look and feel of the task list page.