Add fileSelectionHandlerOptions option to FileInputView

Allow supplying further options to be passed in the payload to allow
the file selection handler to determine its referer dynamically.
Add returnToTab option to PageConfigurationFileSelectionHandler

By default one returns to the files tab after selecting a file to be
used in a page. This option allows to specify a different tab to
return to.
Make TabsView ignore unknown defaultTab

Do not fail if the `defaultTab` references an unknwon tab name. Use
first tab as fallback.
Merge pull request #166 from tf/improve-tabs-view

Improve TabsView