The aprs string only contains time information, no date.
Manual date correction is applied +-one hour around midnight.
Thus, packets older than one hour are dropped.
This change enables us to define a custom callback which is
called when the gateway receives a packet
(e.g. save the incoming beacon in a database and generate
some statistics/aggregate data).
The documentation[1] says:
> In the simplest case, __init__.py can just be an empty file,
> but it can also execute initialization code for the package or
> set the __all__ variable, described later.
A class like 'ognGateway' can't be considered 'initialization code'.
[1]: https://docs.python.org/3/tutorial/modules.html#packages