AbstractSmrPlayer: add missing property declarations
AbstractSmrPlayer: add missing property declarations

Add properties `forceDropMessages`, `groupScoutMessages`, and `canFed`.
This fixes the Scrutinizer warnings, e.g.

> The property `forceDropMessages` does not exist. Although not
> strictly required by PHP, it is generally a best practice to declare
> properties explicitly.

hemberger/smr,smrealms/smr,smrealms/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr