Add support for Altcha v2 (and more urgently pin to v1)

[violuke]

This package allows for altcha v2 to be installed, but it isn't compatible. Can this be pinned to v1 or support for v2 be added?

Thank you 🙏

[hleroy]

Hello @tdruez @xgimp the pinning of altcha<2 is rather urgent. The current code won't work unless the user pins altcha by himself.