mod_filter_season: add buttons for common season selecting

[smwoodman]

Add a 'select last 5 seasons' option to multi-season filter in mod_filter_season. The default of 'all seasons selected' is a fine default, but too much to delete through.

Other option would be to have the default be the last ~5 seasons, and provide a button for 'select all seasons'.

Thinking out loud, maybe providing two buttons for both options is the most user-friendly, no matter what the default ends up being.

[smwoodman]

Potential buttons to add:

• select last 5 seasons
• deselect all seasons
• select all seasons
• select all AMLR seasons (ie, not Costa project 'seasons')