Replaced attached properties with hidden database

[da-h]

#Replaced attached properties with hidden database
Attention: This is a breaking change.

This MR changes the way miniflask saves data that relates to the wrapped event functions.

Previously:

• Wrapped events (functions or classes) were decorated with attributes that specify how the callables are used to construct the actual events
• Especially, when using classes this may lead to unexpected behavior

To solve this, the event object now contains a hidden _data dictionary that saves this information.
New Behavior:

• event._data[eventname] contains the dictionary with all information required to construct the events
• event._data[eventname]["modules"]: list of modules that define the event eventname
• event._data[eventname]["wrapped_event"]: symlink to event.eventname
• event._data[eventname]["wrapped_single_events"]: list of all wrapped events in case of non-unique event eventname
• event._data[eventname]["raw_functions"]: list of all raw functions (as defined in code) in the modules given above (same order as in the modules list)
• event._data[eventname]["raw_function_args"]: the mf, state and event objects arguments needed for the raw functions

Check all before creating this PR:

• Documentation adapted
• unit tests adapted / created