fix: duplicate queries.json file generation

[MaximStockmans]

Closes #145

Problem

The queries.json file was generated twice, once in the current working directory and once in the build directory. The file was first generated in the current working directory, and then passed to webpack for bundling. This bundling copied the file to the build directory, causing the file to exist twice.

Solution

Removed the queries.json file from the entries in the webpack plugin and instead wrote a custom plugin that moves this file into the build folder when webpack is triggered.

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[rubensworks]

Thanks @MaximStockmans!
Feel free to claim the bounty via https://opencollective.com/comunica-association ! (you can add VAT if needed)