SkyWallet environment

**Feature description**

Enumerate available hardware wallet devices .

**Is your feature request related to a problem? Please describe.**
There is no support for using connected hardware wallets not bound to an existing (local or remote) SkyFiber wallet.

**Describe the solution you'd like**
Enumerate hardware wallet devices not related to existing local wallets so that they may be selected in wallet list for doing common operations .

**Describe alternatives you've considered**
Skycoin (electron) desktop wallet puts hardware and local wallets explicitly apart . Duplication over-complicates user interface .

**Additional context**
Needs a remote node .

As a rule of thumb this environment shall only enumerate hardware wallets configured with a seed not matching any of the local and/or remote wallets in the list . In case of a coincidence the hardware wallet shall only be considered as an attached signing device ( see #139 ) .

Implementing connect / disconnect might need changes in core interfaces .

**Possible implementation**

Shares a lot of functionality in common with local wallet implementation . Differences are

- ~Implement signing with SkyWallet~ reuse code for #139
- [ ] Implement address sequence with SkyWallet
- [ ] Implement plug and play connect and disconnect events