roots_tags: Accept *args and **kwargs for url_active tag
competitions: Add migration for UserSolution.solution field
competitions: Change SeasonListView to SeasonDetailView
roots_tags: Add access filter that accesses a dictionary field
problems: Fix get_solution_path in UserSolution

The get_solution_path did not accept any positional or keyword arguments
resulting into error when called upon to generate the name of the saved
file from the previous name.
problems: Do not use str-ed keywords for solutions dictionary in the SeasonDetailView

This was an remainder of an useless workarond of a problem that was casued
by something else.
competitions: Differentiate between submitted and not submitted problems in SeasonView
competitions: Show problems past the series deadline as not submitted in the SeasonDetailView
leaflets: organised views update