Database dump option - enhancements

[mennodekker]

Added code that does this for Gemstracker specific.
It takes all tabels in Gemstracker and can create a mysql dump from it. Currently hardcoded are the tables that are safe to export as they do not contain any sensitive data.
The mysqldump file gets stored in a specific folder, but currently is not downloadable in the interface.
In some environments it can be safer to call this controller on the commandline, as it can take a while to process.

Possible improvements:

• Possibly add the whitelist of non-respondent data to a table or as prefix comment to the sql files.
• Add something similar for limesurvey sources.
• Maybe a separate option to whitelist staff accounts?
• Add option for compression (e.g. gzip the .sql output)
• Possibly add other options from the mysqldump-php library

Originally posted by @jvangestel in #435 (comment)

[mennodekker]

It might be good to at least create a way to delete backups from the interface. Downloading is a risk, but in some setups the created files can not be deleted by the one downloading them.

If it is possible to split in smaller (appending) chunks and create a task for this the timeout won't be a problem anymore. This would break the single transaction.

[mennodekker]

I noticed a nice function to filter data on export: https://github.com/ifsnop/mysqldump-php#table-specific-export-conditions could be nice to export more data while still keeping security and privacy in mind.