Simplify contact import

[stv0g]

We should provide a way to mass-import your phonebook.

Previously, this was done by using Google APIs to fetch Google Mail contacts (which are synchronized to the phone for most users).

However, I removed this feature because it was broken and the fact that I don't like to support Google products anymore. I don't want not promote the usage of Google Mail to sync your contacts!

What to you think about sending your contacts via CardDAV file to the bot? The bot then extracts all numbers and syncs them with the WhatsApp servers.