Revision on https://github.com/odoo/odoo/commit/32b8cec5361174c92c45a4975d4e02f1fb448aa2

Before this commit, when we switch channels in the Discuss app, the breadcrumb
was visually not updated: it keeps the name of the first opened channel.

With this commit, the breadcrumb is updated on each change of channel, so that
it displays the name of the currently opened channel.

Technical details:

	This is due to a change of logic of updating the GUI of the breadcrumb:
	before the refactoring above, discuss had to pass the content of the
	breadcrumb to the control panel, in order to update the breadcrumb visually.

	After the refactoring, the action manager should warn the control panel to
	update the breadcrumb on any change of the title. This is already the case
	for `ir.actions.act_window`, but not for all types of client actions.