Add JS source maps

Resolves #342 (closed)

Laravel Mix should now output source maps. Read the issue for the proposal.

File Sizes

The size of the source maps may be alarming. However, these files are meant for developers only and will only ever be loaded when DevTools are opened. This should not affect user performance in any way.

Sources:

• https://stackoverflow.com/a/40860968
• https://css-tricks.com/should-i-use-source-maps-in-production/

To test it yourself

1. Write a console.error somewhere in the code
2. Run yarn production
3. Navigate on the website to where you would see this console.error
4. Look at console, the error message should be pointing to the source code at the correct line number (as opposed to the usual solstice.js line 2)