Avoid repeating `npm install` on each exercise

Some people find it tedious and a waste of time to have to install NodeJS packages everytime they want to solve an exercise (take a look at exercism.io#2972).

In that discussion, we reached to a solution: improve the documentation on /docs/INSTALATION.md to guide users to install all dependencies on <EXERCISM_HOME>/ecmascript and add that folder to the PATH system variable. This way, all mandatory tools to run tests will be available on the path and there will be no need to npm install on each exercise.

[aeamaea]

At 3kg / GB , it’s about 3000kg / TB or 240,000 kilograms (half a million pounds) of carbon contributed to the atmosphere, just by the Javacript track on exercism.

It’s probably peanuts compared to all the Netflix streaming that’s going on, but I’m going to leave it out here anyway.

https://www.emergeinteractive.com/insights/detail/does-irresponsible-web-development-contribute-to-global-warming/

[aeamaea]

It’s kinda hokey, but I just move the node modules from the completed exercise to the new one before running npm test for the first time. In all honestly, the base module set could just be cached and moved to each exercise as it’s fetched and any deltas would be downloaded by npm anyway. seems to work for me. It’s a huge waste and has an unacceptable environmental footprint as well. by the end of the JS track, each user would’ve download 9.5 gigabytes worth , multiply that with 86000 students (at the time of this writing) and you potentially have about 80 terabytes of node-modules down the wire that didn’t really need to be downloaded. I’ll leave the carbon footprint calculations for those who are interested in such things.