Installing lunr search capability

2022-07-06/07/10 including lunr search

Steps to incorporate lunr search from developer-massive-wiki to another massive-wiki (running MWB v1.9.0):
0. merge (done manually)
1. install node modules:
- install node (e.g., macOS: $ brew install node)
- copy package.json, package-lock.json to .massivewikibuilder
- $ npm ci (this installs the node modules into folder node_modules)
2. install build-index.js in .massivewikibuilder
3. in this-wiki-themes/basso: update page.html, _navbar.html, search.html
4. merge (done manually - a simple copy may do it)
5. update netlify.toml (add --lunr to the mwb build line)