Silva-security-logging

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* ...

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* Remove debug warning.

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* Make sure that entries contains only strings, in order to create
valid SQL queries.

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* Make sure the code works on both Silva 2.3 and 3.0.

* Disable logging during upgrade operations (for speed).

* Prevent breakage when storage is misconfigured.

* Add possibility to configure table name with SQL storage.

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* Update code for Silva 3.0.

* Add more events to by logged (there are more in 3.0).

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* Initial release.