enhance functionality of InnerWindow

[roffe]

Description:

2 changes:

First:
allow customization of button location on InnerWindow via InnerWindow.ButtonAlignment

The widget.ButtonAlign constant is used to configure

ButtonAlignment specifies where the window buttons (close, minimize, maximize) should be placed.
The default is widget.ButtonAlignCenter which will auto select based on the OS.
- On Darwin this will be `widget.ButtonAlignLeading`
- On all other OS this will be `widget.ButtonAlignTrailing`

Second
Added Title() string function to retrieve the title of the current inner window

[coveralls]

coverage: 60.012% (+0.04%) from 59.974%
when pulling b9ca162 on roffe:roffe/multiwindow
into a1d708d on fyne-io:develop.

[Jacalz]

Would it make sense to default to buttons on the right side on Windows and Linux? Windows seems like a rather simple choice but Linux has more customisation of course. However, with all the major Linux vendors distributions like Ubuntu and Fedora defaulting to the right side it seems like a sensible choice?

[roffe]

that should do it

[andydotxyz]

Would it be OK to re-use the existing button align consts?

[andydotxyz]

A nice addition, thanks

All new APIs need the:

//
// Since: 2.6

lines at the end of their documentation

[Jacalz]

For the record: I realised that my comment about Fedora defaulting to buttons on the right side is technically incorrect, at least on Gnome. Anyhow, Ubuntu is the largest and they default to the right like most other :)

[Jacalz]

Thanks. Some minor comments inline :)

[Jacalz]

Sorry, I realised that I missed some things in my last review

[andydotxyz]

Hi @roffe, it's not clear why this was deleted, was it a mistake?