HardwareView: Make hostname editable

[ryonakano]

Fixes #248 Fixes elementary/switchboard-plug-sharing#53

Pressing Enter key in the entry now sets the hostname.

Currently we show the hostname only when the hardware is not made by OEM. So, I separate the widget that shows either hostname or the product name into two different widgets.

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With OEM info, successfully acquired the Polkit permission to edit hostname:

Without OEM info, failed to acquire the permission:

[danirabbit]

I wonder if we also need to add something about a restart being required? It looks like for example Bluetooth sharing name isn't change until we restart