[FIX] Make the printscreen links appear even in grouped view

We've had an issue where the "PDF or Excel" link isn't shown in grouped views, since it is added to the oe_pager_value div, which is set to display:none in that case.

This changes how the link is added and instead:
* Puts both links in a "ListView.ExportLinks" template
* Changes ListView.load_list() to add the rendered ExportLinks template after the pager div
* Toggles visibility of the links in the view manager's switch_mode() function/