Panel's foreground is inherited to all contained styled labels

[mgarin]

@Sciss mentioned on our discussion on Gitter that whenever panel's <foreground> setting is specified - all styled labels (and some other text components) inherit that foreground color.

I already did some investigation and there are multiple reasons that cause such behavior:

1. AbstractTextContent only uses it's own color from the style if there is no non-UIResource color specified in component's foreground
2. WebStyledLabel actually doesn't have it's own foreground, it's basically null for it
3. All colors deserialized from the style right now are NOT ColorUIResources but simple Colors
4. All Swing components actually inherit multiple settings from parent, including foreground, background and some others, here is a foreground code piece from Component:

    public Color getForeground() {
        Color foreground = this.foreground;
        if (foreground != null) {
            return foreground;
        }
        Container parent = this.parent;
        return (parent != null) ? parent.getForeground() : null;
    }

All these reasons together cause the mentioned behavior.

There are a few things that have to be done to fix this and avoid such issues in the future:

1. Ensure that all Colors read from style are read as ColorUIResources
2. Probably specify default foregrounds for text components in style instead of the L&F as it is to an unreliable source and also doesn't account for the current skin
3. Adjust text component styles accordingly

[mgarin]

There were a few more issues on top of mentioned above that I've found while trying to fix this.

One of the issues is that disabled colors from style would not be prioritized anymore if user would set, let's say, a JLabel foreground - that foreground will persist for disabled state as well because it is not a UIResource and the current text content implementation always favors non-UIResource options to avoid having user settings overwritten by the style ones. I will fix this by adding a separate setting to ignore user color for particular states - for instance for disabled states.

There is also an issue with WebDocumentPane tab colors being inherited from the parent despite the fix I've made for it. It happened because it overwritten foreground with null value and forced tab title to inherit color once again.

And there is also an issue with WebTabbedPane tab titles not respecting colors specified through setForegroundAt ( int, Color ) - this will get patched by custom text contents for the Tab element in the style (it is basically a styledlabel used as tab title).

I'm wrapping up with the last fixes right now and hopefully will soon push the fix.

[mgarin]

I've fixed the main issue and all of the related ones.
Hopefully there should be no more weird cases of color inheritance anywhere by default.