GitLab

use case:

Just configured and installed a node.

benefits:

1) reduces friction when setting up a new node

2) reveals useful details about the workings of the system. It's the
user's first encounter with her node's identity. The tour can build on
the user's knowledge.

```
ipfs (maybebtc-november) λ. ipfs init -f
initializing ipfs node at /Users/btc/.go-ipfs
generating key pair
peer identity: QmcRbn41Vc2CvbpLYfN36mAWusErKWvAAHbq92LPra2gFT
```

Removed config.Filename and replace it with config.GetConfigFilePath that
takes a configuration directory as argument instead. Makes code simpler.
ipfs.getConfigDir now also return the default configuration dir instead of
an empty string in some cases.

WARNING: change breaks old configs.
@whyrusleeping @perfmode

This commit changes the way addresses are stored in config files.
It lumps Identity.Address and RPCAddress into Addresses. This
commit also fixes several golint issues.

There are (so far) two sorts of addresses that peers care about:

- peer network addresses, local to listen, saved to bootstrap.
  `config.Identity.Address`

- peer RPC network address, local RPC tcp endpoint
  `config.RPCAddress`

@whyrusleeping @perfmode

In the future, let's have a (signed) list of bootstrap
nodes. Ideally just a list of ipfs multiaddrs (with node.ID)

also replace *Datastore with Datastore