chore(linux): Update Keyman Configuration to match Gnome Human Interface Guidelines

* Should remember size and location
After closing and re-opening, the window moves back to a default size and location. This is particularly unhelpful when a keyboard installs, as the window quits for a second before re-opening, then moving back to its default location
https://developer.gnome.org/hig/guidelines/adaptive.html

* Remove close button
In the main window, there is a close button in the bottom left. This is unnecessary, as the window can simply be closed by the default close button in the top right.
https://developer.gnome.org/hig/patterns/controls/menus.html

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* Remove the close button and move the back button to the top in the Download Keyboard dialog.
The close button is again unnecessary, as it can be closed by the default button. The back button should also be moved to the top, and the bottom bar, removed.
https://developer.gnome.org/hig/patterns/controls/menus.html
https://developer.gnome.org/hig/patterns/feedback/dialogs.html

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* In dialogs, cancel and continue buttons should be in the top bar. Not the bottom one.
In the installing keyboard dialog, and the keyboard installed dialog, the buttons are in a bottom bar. These buttons should, again, be moved to the top bar.
https://developer.gnome.org/hig/patterns/feedback/dialogs.html

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* In dialogs, the continue button should start selected, not the cancel one.
https://developer.gnome.org/hig/patterns/feedback/dialogs.html

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* Keyboard shortcut help (crtl+?)
https://developer.gnome.org/hig/reference/keyboard.html