Allow SQLite files in WoF-Root

[arnesetzer]

👋 I did some awesome work for the Pelias project and would love for everyone to have a look at it and provide feedback.

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Here's the reason for this change 🚀

Follow up on pelias/whosonfirst#557 to also allow the placeholder to use sqlite files which are not in the sqlite directory.

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Here's what actually got changed 👏

The 'WOF_DIR' variable is now a string array set to '[config.datapath, config.datapath.sqlite]' if 'process.env.WOF_DIR' is not set. The correct path for each file is determined and saved for importing from both directories. The same logic applies as in pelias/whosonfirst#557: if a file with the same name exists in both the root directory and the sqlite directory, the sqlite file will be used.

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Here's how others can test the changes 👀

1. Check out the PR.
2. Put some files in the WOF root directory/sqlite directory.
3. Run the command 'npm run extract' and check that all databases have been imported into wof.extract.