Modify bot: support multiple config files

[ghost]

We currently have two config files which do overlap each other. In the future

• the number of rules will increase (e.g. with a more complete malware name-family mapping) and consequently
• not all rules are useful for all users.

So I think we need to split these configuration parts into more files.

My idea is that the bot itself could resolve globs in the filename (e.g. /var/lib/intelmq/bots/modify/*.conf) and read them all.

[chorsley]

I noticed this just after logging it, but #1026 is another proposal addressing the same issue.

[ghost]

current example is smaller now because of the malware name mapping