`ipfs pin ls` should list recursive pins only by default

Currently, `ipfs pin ls` will list all pins.
This is an expensive operation and it seems like most people want `ipfs pin ls --type=recursive` anyway.
I propose that we change this so that recursive pins are listed by default (`--type=recursive`), and `--type=all` should be explicitly required for listing all pins.

Even if we make listing all pins fast, @lgierth points out that `ipfs add` pins objects recursively by default. So we may want to still do this anyway for consistency's sake.