Create minimal view algorithms

Potentially we need the ability to just encapsulate a set of algorithms in an EventView, and then retrieve outputs from that view. Currently this is motivated by the full scan HLT chains interfering through intermediate tracking objects.

The current view algorithms assume creation and merging of multiple views, and their interaction with the trigger navigation. So, I have added extremely minimal algorithms that only do the task above.

NB: there's a slightly long-winded chain of edits in StoreGate, just to make a private method public, allowing typeless aliases to be created.