ui: user with no workflows can't see shared workflows

[mdonadoni]

Currently, if a user has never run any workflow, but some other user has shared workflows with him, he will not be able to see the list of shared workflows, as the homepage will instead show the welcome message:

reana-ui/reana-ui/src/pages/workflowList/WorkflowList.js

Lines 125 to 127 in 660584e

	if (!hasUserWorkflows) {
	return <Welcome />;
	}