Transition from Phosphor CSS class names to Lumino names

[vidartf]

In the "controls" JS package's CSS we still have references to PhosphorJS CSS class names:

ipywidgets/packages/controls/css/widgets-base.css

Lines 1289 to 1291 in 1b1a49d

	.jupyter-widgets.jupyter-widget-tab > .p-TabBar .p-TabBar-tabIcon,
	.jupyter-widgets.jupyter-widget-tab > .p-TabBar .p-TabBar-tabLabel,
	.jupyter-widgets.jupyter-widget-tab > .p-TabBar .p-TabBar-tabCloseIcon {

Mostly this seems to be .p-Tabbar related or .p-mod. By the time that JupyterLab chooses to drop the deprecated phosphor classes, we will need to update our CSS to either support both names, or to only support the Lumino class names.

[jasongrout]

We also have some p-* css classes we add.

ipywidgets/packages/controls/src/lumino/tabpanel.ts

Line 114 in 1b1a49d

this.addClass('p-TabPanel');

ipywidgets/packages/controls/src/lumino/tabpanel.ts

Line 118 in 1b1a49d

this.tabBar.addClass('p-TabPanel-tabBar');

ipywidgets/packages/controls/src/lumino/tabpanel.ts

Line 120 in 1b1a49d

this.tabContents.addClass('p-TabPanel-tabContents');

I agree that this is confusing and should be switched over to either lm-based classes or perhaps our own prefix for our own classes that we are adding.