add email signature generator

mail_signature/__init__.py

mail_signature/admin.py

mail_signature/apps.py

mail_signature/migrations/__init__.py

mail_signature/models.py

mail_signature/templates/mail_signature/index.html

mail_signature/tests.py

mail_signature/urls.py

mail_signature/views.py

package.json

rv_voting_calc/templates/rv_voting_calc/index.html

rybicka/settings/base.py

rybicka/urls.py

shared/static/shared/signature.webp

shared/templates/shared/index.html

static_src/mail_signature.js

tailwind.config.js

webpack.config.js