[virt-tools-list] virt-manager XML editing UI WIP

[Cole Robinson]

I published a virt-manager branch with some inprogress work to add a raw
XML editing UI. The code is here:

https://github.com/crobinso/virt-manager/tree/uixml

The implementation is a bit hacky right now, there's still some internal
API bits that need some thought. That branch adds it for:

* Editing <network> XML in Connection Details
* Editing <pool> XML in Connection Details
* Editing device XML in addhardware

There's some screenshots here: https://imgur.com/a/fduqpv6

It's structured as a gtknotebook with two tabs

* 'Details' which shows the existing UI in the above cases
* 'XML' which switches to a GtkSourceView with the XML

It reuses the existing UI 'apply'/'finish' buttons to actually commit
the changes. If you edit the 'XML' and try to switch tabs before
'apply'ing we warn that changes will be lost, because we don't really
have any way to switch back and forth between editing individual XML
fields and editing the XML raw. It's not the nicest looking thing but
it's the best I could think of that's a reusable UI pattern, and
reusable means it simplifies wiring this up everywhere else.

The remaining places this can be added:

* Details dialog for the whole <domain> XML
* Details dialog for individual device XML pages
* createnet dialog
* createpool dialog
* createvol dialog
* clone dialog?

I'll also be generating a list of UI bits that I think we should drop
once this is in place. That will be a separate mail at some point. But
possibly: <network> QoS editing, <disk> driver io, <disk> driver type,
<disk> serial, <interface> vport stuff, likely some <graphics> options.

Also I think we should slim the createnet and createpool dialogs down to
a single screen, possibly with a pattern like the addhardware wizard
with a single list on the side for choosing pool or network types. This
scales better, but also by limiting to a single screen will force us to
make sure the exposed options aren't out of control and taking up too
much real estate.

Comments welcome

Thanks,
Cole