refactor: update js files to typescript and replace parcel with rollup

- add basic rollup config to bundle minified and browser compatible js
- use babel to transpile
typescript files to js
- add static code checkers: eslint and stylelint
- update package.json
scripts
- update DEPENDENCIES.md file to include rollup and popper
- set html in rss feed
description fields
- update Podcast and Episode entities to add description_html attribute
generated by parsing markdown to html using parsedown

#9