Welcome dialog 1.1.x: no option to just keep current settings for theme

Summary:

The Welcome dialog in 1.1.x does not offer any option to just keep current settings for the theme, which might alienate users who carefully already selected a theme for themselves.

Clicking on 'Save' in the first tab will break the currently carefully selected theme of 'old' Inkscape users, as the option to just not make a change is not visible (like 'Cancel', 'don't change' or 'Keep current'). It's not obvious that that part of the dialog can just be skipped.

@jabiertxof @doctormo I had understood that you wanted to implement that option?

Steps to reproduce:

• open Inkscape 1.1.x for the first time
• get 'Default' offered as theme, even if you've already selected a different one in your previous installation.
• Click on 'Save' as there seems to be no other option but to change your theme to any of the predefined themes, which you may also not want.

What happened?

• Be annoyed by the first impression, because you get greeted with ugly icons and interface, while you had already decided upon that earlier.

What should have happened?

The default option should be to 'not change current setting' (keep current, don't change).

If that's not possible, due to the dialog combining parts of the theme in ways that are potentially incompatible, instead a button should be added that says 'Cancel' or 'Keep current theme'.

Inkscape Version and Operating System:

• Inkscape Version: Inkscape 1.1-beta1 (4738257183, 2021-04-29)
• Operating System: Linux Mint 20.1