Add CORS so API can be queried programmatically

[GarrisonBates]

Describe the bug

Get CORS error when querying API. Please enable CORS for all domains for Raptoreum explorer. Thanks!
Environment (please complete the following information):

• Bitcoin Core / Node Version [e.g. 0.16.3]
• NodeJS Version [e.g. 9.x]
• Browser [e.g. chrome, safari]
• Code Version / Commit [e.g. ab6cde8]

Configuration file content

Please include the content from the following files. BE SURE TO MODIFY YOUR CREDENTIALS BEFORE SUBMITTING!!!

• bitcoin.conf
• Your btc-rpc-explorer environment configuration (either $WORKING_DIR/.env or ~/.config/btc-rpc-explorer.env)

To Reproduce

Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Screenshots or Log Output

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Additional context

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