Custom python decorators with global functions without arguments

[meevee98]

See #574

A very simple use case I can think of would be to implement something like that:

from boa3.builtin import CreateNewEvent, public
                                               
def onlyOwner(): 
    # do owner check and abort if false                              
    pass                                       
                                               
@onlyOwner                                     
@public                                        
def withdraw() -> bool:                        
    pass                                       

Only decorators that calls global or imported functions without arguments is going to be implemented in this issue

[luc10921]

It's not possible to create a decorator without a parameter