Avoid using both Yarn and NPM

Having both `yarn.lock` and `package-lock.json` (i.e. using both Yarn and NPM) could [easily](yarnpkg/yarn#5654) [be](yarnpkg/yarn#3614) [problematic](https://stackoverflow.com/questions/44552348/should-i-commit-yarn-lock-and-package-lock-json-files). In short, it creates a risk of out-of-sync where one author installs with NPM and forgot to update yarn.lock so another author, when using yarn, won't have that dependency.

In this PR I propose to drop the use of yarn in favor of NPM since a search in the codebase yields more NPM usages (especially in the doc and in package.json) than Yarn (only in Docker file to install).

If others have strong reasons for using Yarn over NPM then feel free to yield them. I don't have strong personal reason for one over another :D

Author: jmohan57

Dockerfile

@@ -10,13 +10,12 @@ RUN curl -sL https://deb.nodesource.com/setup_12.x  | bash -
 RUN apt-get install -y --no-install-recommends nodejs && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/*
-RUN npm install -g yarn
 
 ADD requirements.txt .
 RUN pip install -r requirements.txt
 
 ADD package.json package-lock.json ./
-RUN yarn install
+RUN npm instal
 
 # ENV should be configure from outside
 # @see docker-compose.yaml