Use HTTPX instead of Requests in Python templates

[vdusek]

Issue

• https://github.com/apify/actor-templates/issues/182 The motivation for usage of HTTPX is explained here: https://github.com/apify/actor-templates/issues/182#issuecomment-1748615100.

Description

• All the templates that were using Requests (python-beautifulsoup, python-start) now use HTTPX.
  • I also updated relevant texts in the readmes and in the code comments.
• On top of that...
  • I removed beautifulsoup from the requirements.txt of python-empty template (it was not used there).
  • actor -> Actor
  • Fix a few broken/wrong links (e.g. to JS instead of Python docs)
  • Some unification of ## Included features section in the README across all the Python Actors