[bunq] Add plugin for synchronisation with bunq bank

[hello-foma]

Features:

• Login using api-key (accessible from the bunq app)
• Sync accounts and transactions
• Ignore "investment" accounts as they are don't have proper balance and transactions
• Merge transfers between own bunq accounts

[hello-foma]

@skvav Is there anything that I can help to move this plugin forward?

[skvav]

@hello-foma Hi! Thank you for your contribution. The only question so far is whether it is better than current GoCardless based implementation and why? :)

[hello-foma]

@hello-foma Hi! Thank you for your contribution. The only question so far is whether it is better than current GoCardless based implementation and why? :)

The problem is that synchronisation is not working: the result is always zero accounts and zero transactions.

I've sent a log through Zenmoney app.