Make a cache resistant flash

[dNitza]

We need a way to create a persistent flash hash without doing anything tricky to the existing roda flash plugin lest that bight us later on or should we want to extract this cache resistant flash behaviour to a standalone gem.

# roda_plugins.rb
def view(name, overrides = {})
  # do something to persist flash in a seperate persisted_flash hash here perhaps
  overrides[:with] ||= {}
  options = {scope: scope.current_page(overrides[:with])}.merge(overrides)
  is(to: "main.views.#{name}", call_with: [options])
end

then later access the persisted_flash via ajax and clear it as needed.