New directory structure

[arkpar]

This PR introduces a new directory structure for Paritys' files. The new structure looks like this:

.parity
  chains
    ethereum
      db
        906a34e69aec8c0d
          snapshot
          overlayrecent
            version
            db
              *.sst
          archive
            version
            db
              *.sst
      network
        nodes.json
      user_defauls	
    classic
    test
  keys
    ethereum
    test
    classic
  signer
  dapps
  ipc

• --db-path and -d now set a root path for all files (.parity alternative).
• db kill command is introduced.

Closes #3683, #1221, #2383, #2374

[coveralls]

Changes Unknown when pulling 85fd629 on new-dirs into ** on master**.

[rphmeier]

Seems to also close https://github.com/ethcore/parity/issues/2383

This seems much better. I assume the config file will go in ~/.parity/ root as well?

[rphmeier]

This seems to break compatibility with previous chain specs.
Also the doc string here is now wrong.

[arkpar]

Don't think anyone uses this for private chains. We use it for classic and expanse. Upgrade path for these is supported.

[rphmeier]

nit: whitespace

[arkpar]

Config goes into ~/.parity/ by default.

[coveralls]

Changes Unknown when pulling 5fd2e15 on new-dirs into ** on master**.

[gavofyork]

would be good to solve https://github.com/ethcore/parity/issues/1648 in this PR too since they both need paths sorting.

[rphmeier]

having --db-path default set using app_dirs crate seems simple enough:

let app_info = AppInfo { name: "parity", author: "parity" };
let db_path = try!(get_app_root(AppDataType::UserData, &app_info));

[rphmeier]

It even obeys XDG base dir standards :)

[coveralls]

Changes Unknown when pulling be5fefe on new-dirs into ** on master**.

[coveralls]

Changes Unknown when pulling 3280f07 on new-dirs into ** on master**.

[gavofyork]

maybe make -d / --root-path -> for the root data directory ($HOME/.parity or whatever); --db-path -> just for the chain/state databases; --keys-path -> for keys, ...