Change default value of webserver.threads to 50

[DL6ER]

What does this implement/fix?

Change default value of webserver.threads to 50, make 0 behave as if the user has set 50 (for backwards-compatibility reasons) and remove the upper limit we enforced on the number of threads.

This should improve the webserver/API's performance especially of single- and dual-core machines.

The word of warning I have for this change can be read here: #2284 (comment) I guess we still want to do this. We also updated CivetWeb in between (and I will shortly put up another update to their current master), so the original issue may really have been fixed.

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Related issue or feature (if applicable): Fixes #2284

Pull request in docs with documentation (if applicable): N/A

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[yubiuser]

Did you target master on purpose?

[DL6ER]

No...