Docs: CI & minor improvements of contents

[jdupak]

• Initial version of the User Manual in simple MarkDown format
• Docs: Add mdbook support for user manual
• CI: Deploy user manual as github pages
• Docs: integrate old user docs into the new user manual
• Docs: move manual to user
• Docs: minor structure change
• Docs: update instalation manual
• Docs: move to manual url
• CI: Fix run rules for docs.yml
• Docs: fix mdbook summary format
• CI: fix docs change tracking
• CI: Avoid running debug CI for docs change only
• GUI: Add help link to the manual and report problem button
• Docs: Add project links to manual
• CI: Remove temporary branch for building docs