2249: Create a global stylesheet and allow user-built themes

[krzywon]

This PR is creates a centralized style sheet for all GUI widgets, has the start of two other themes that are currently disabled (Dark and Large Font), and allows for user-created themes.

Current functionality:

• Sets a single style sheet for all GUI elements and alternates to modify background colors, fonts, etc.
• Built-in style sheets are not (easily) accessible by the user
• Replaced all setStyleSheet, setFont instances with a standardized GuiUtil method
• Added the option for users to add their own themes
• Added a preference to select a theme from the available options

Future features:

• Document the system
• User documentation for creating themes
• Finish dark and large-font themes (and any others?)

[lucas-wilkins]

I think there needs to be a bit of thought about how this will work if we want, say, the ability to change the font size as a user-friendly setting.

[pkienzle]

I don't think you want a user-controlled style sheet. I expect that old .css files will be a support headache down the line.

Instead I suggest putting the default style sheet as a resource much like an image file. We can document its location so that interested users can override it, but their changes will be gone with the next install.

[krzywon]

There are now 4 themes. This should be ready for a full review.

[lucas-wilkins]

Anything I need to do for the corfunc bit?

[krzywon]

Anything I need to do for the corfunc bit?

Maybe have a check to see if I missed any inline styles, but I was able to pull many of them out.

[lucas-wilkins]

Much better, still need to do something about the window borders, they appear to take the system theme.

[lucas-wilkins]

Dark theme disabled and unchecked boxes are pretty much indistinguishable on my screen.

[lucas-wilkins]

Other minor points: the check/radio boxes should not be white, and the blue non-focus color is very blue. The white font is too white too.

[butlerpd]

Actually could be part of 6.0 .. but maybe a lower priority? Should take a look at

[rozyczko]

hmmm these look like a downgrade from the existing style.
The default stylesheet looks pretty bad now.
Checkboxes look less intuitive.
Font clarity is much worse.

NEW:

OLD:

NEW:

OLD:

[lucas-wilkins]

Pyside6 now natively supports dark and light themes, inherited from the OS.