Add ability to prevent certain mode's buffers from being stored

e.g., ```*eshell*``` buffers are restorable just fine whereas ```*shell*``` buffers are not (among others, e.g., python process buffers https://github.com/alphapapa/burly.el/issues/30).

I apologize if ```bookmarks``` can already do this but I can't find where. I'm not really sure what a good solution is beyond crafting a default noop ```bookmark-handler``` that can be associated with modes that do not support bookmarks or ```advice``` around ```bookmark-default-handler```. Or an ```activities``` configuration option that would take a list of buffer name regexp patterns and another list of modes to ignore, perhaps modeled after the way ```ibuffer-saved-filter-groups``` works?

Related: #30 #39 #40