#2011: Use group identifier as Communication:To in group messages

[lfcnassif]

Closes #2011. This can have a big impact in case disk size and processing time when groups with many members and messages are decoded from IM applications.

I would like someone else to review this, since it will change the output of some chat decoders (Telegram, WhatsApp, Threema, Discord, Skype, UFDR imported chats).

@hauck-jvsh could you take a look after you return from vacation?

@aberenguel, could you test this with the UFDR you mentioned on #2011?

[lfcnassif]

2 users tested this and it fixed the exponential time and space usage behavior with past cases which processing never finished.

@felipecampanini could you please confirm if commit 1d676d8 in DiscordParser is good? I used the Chat name as TO, not sure if it is fine, ideally it should be a discord forum/thread unique name/identifier, to avoid merging different groups/forums in the graph view as the same entity.

@patrickdalla could you please confirm if commit 53c5a3c in SkypeParser is fine?

[lfcnassif]

Another user tested this PR and it worked fine, resulting in great processing time and case size reduction, like the other 2 users noticed, so I'm merging this. @felipecampanini and @patrickdalla, if groups identification in DiscordParser and SkypeParser could be improved, please let me know.