Components: [Tabs] Export all tab components to allow extending

[nop1984]

Bug, feature request, or proposal:

feature request

What is the expected behavior?

Extending the MatTabGroup

What is the current behavior?

not possible to extend MatTabGroup because of MatTabBody and MatTabHeader and MatTabLabelWrapper are not included in module export list

What are the steps to reproduce?

Try to extend MatTabGroup to add tab close icon and function. You will get errors like "ERROR in : Can't bind to 'selectedIndex' since it isn't a known property of 'mat-tab-header'." to your overloaded template of MatTabGroup class

What is the use-case or motivation for changing an existing behavior?

Because having a static Tabs is not enough. I want to repoduce MDI behaviour where each tab will contain a named router-outlet of links which invoked by other components of application. And ofcource user must be able to close tabs he have opened before

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

all is latest to current date

Is there anything else we should know?

There is only few string to add in @NgModule section to export: [] here https://github.com/angular/material2/blob/master/src/lib/tabs/tabs-module.ts

[nop1984]

@jelbourn , @josephperrott , @andrewseguin FYI, please take a look

[Dorkside]

This would be greatly appreciated