Componentization, adding 3rd party libraries and further setup

[ViorelMocanu]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context. List any dependencies that are required for this change.

Improves #12, #16, #17, #18, #19, #28, #33, #34, #37, #41
Fixes #30 and #31

Type of change

Please delete options that are not relevant and tick with an x the one that is.

• Bug fix (non-breaking change which fixes an issue)
• Content update (text or image-related updates)
• Design update (UI design and static template related change)
• New page (addition or major edit for an existing page layout)
• Documentation update (improvements or additions to documentation)
• New feature or enhancement (non-breaking change which adds functionality)
• Operational update (changes to configuration, CI/CD, procedures, etc.)
• Security update (a fix or update required to alleviate a cyber security issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Changelog

• expanded .gitignore and readme.md
• added a PR template
• added several temporary test code with _old prefix
• add lite-youtube-embed, @astrojs/prefetch, astro-webmanifest, @astrojs/partytown and @astrojs/sitemap in package.json and configure in astro.config.mjs
• place scripts in proper location outside js/script.js
• add a manual robots.txt file
• finish and use the components: Header.astro, Footer.astro, ResourceList.astro, ResourceTOC.astro, ResponsiveImage.astro
• tentatively add for future review and use the components: Breadcrumbs.astro, Button.astro, CommentList.astro, ContactForm.astro, EmbedAnalytics.astro, EmbedTwitter.astro, EmbedYouTube.astro, LanguagePicker.astro, NewsletterSection.astro, Pagination.astro, ResourceFilter.astro
• extract global layout configs in config.ts
• update content schema
• adopt the Markdown format and add test Markdown content files in all content types / categories
• add empty pages
• edit a few pages and make them dynamic
• add a few utilities to be reviewed and used later
• make Typescript configuration stricter

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have manually tested the newly added functionality with no discernable errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules