Stake functionality (Router)

[jubeira]

The Vault can move BPT without approvals, so we could build a staking functionality in the router that sends BPT to a target gauge on behalf of the user.

This means that the users wouldn't need to approve BPT on the gauge to stake, making it a single step operation (given that the user holds BPT beforehand of course).

We could even make add + stake a single operation as a second step.