added "multiple_actions" option for clickable global animations

added "multiple_actions" option for clickable global animations

This change adds a new option for the "graphicsinfo.conf" file to be
able to explicitly allow multiple event actions for clickable global
animations, which is deactivated by default to prevent unwanted side
effects. This would make it possible to trigger two actions that make
sense when executed at the same time, like triggering the "play" and
"pause" buttons of the tape recorder together, for example.)

The new option works like this (with "global.anim_1.part_1.MAIN" also
being defined):

global.anim_2.part_1.MAIN.anim_event:            click:anim_1.part_1
global.anim_2.part_1.MAIN.anim_event_action:     some.action
global.anim_2.part_1.MAIN.style:                 multiple_actions

global.anim_3.part_1.MAIN.anim_event:            click:anim_1.part_1
global.anim_3.part_1.MAIN.anim_event_action:     another.action

When clicking the first global animation (on the main menu screen),
there might be two or more other global animation which are triggered
by clicking the first animation and which each execute their own event
action when triggered. (The style "multiple_actions" must be defined
for all animations that should *not* stop the chain of event actions
to be executed, so it's easiest to just define it for all animations
that should execute their event actions together when triggered.)

This option can be combined with "passthrough_clicks".