* Added new parameter to TMainDisplayMgr.DisplayViewItem that determines whether view item is displayed in new tab or not.
* Removed debugging code for tab display mode from UMainDisplayMgr unit.
* Minimal changes to FmMain unit to work with revised TMainDisplayMgr.DisplayViewItem method.
* Changed behaviour of displaying certain view items: welcome page never overwrites tabs, history and main view items always overwrite and new snippets and categories always use new tabs.
