feat: Captcha configurable

[ip6li]

Make captcha configurable in application.properties:

app.captcha.login.enabled=false
app.captcha.delete.enabled=false
app.captcha.imprint.enabled=true
app.captcha.password.enabled=false
app.captcha.register.enabled=true

In original code captcha is not implemented for registration, this pull request implements configurable captcha for registration, also.