[FEATURE] Enable use of multiple captchas on same page + validation via stream

[David-Bascom]

Adds two new features to the extension:

• Enable use of multiple captchas on same page: Currently only one captcha is possible per page, because captcha-id is not unique and the JS is included inline instead of using the pageRenderer. Fixed by using the pageRenderer and a small JS – both are only included once.
• Fallback for validation via stream in case curl fails with empty result: There are certain server-configurations where curl is installed but the result is empty due to firewall restrictions. This adds a fallback using file_get_contents() which works in most cases.