Adds ref PR context menus

Adds Open Details to commits & stashes in views

Hides commit graph icon in hovers if plus features are disabled

Optimizes startup flow and churn during discovery

e.g. branches, commits, stashes, tags

* 73 - Graph allow user to toggle some features in settings

* Modified name of "enableGhostRefs" property to be "showGhostRefsOnRowHover" instead

Adds search cancellation to avoid needless calls
Adds search limit setting for the Graph

Adds graph.commitOrdering setting

Until the VS Code marketplace can truly handle pre-releases we can't adopt the current limited pre-release provided by VS Code