* adds lock angle to pen tool
The current [Shift] Break Handle behavior should become Alt instead of Shift
The current [Ctrl] Snap 15° behavior should become Shift instead of Ctrl
Implement the extend-in-this-direction feature called [Ctrl] Lock Angle that exists in the Line tool, but doesn't yet exist in the Pen tool
* avoid clone by passing exlusive ref to tool data field directly
* Rearrange hints
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Co-authored-by: Keavon Chambers <keavon@keavon.com>
* implements pan/zoom to the selected layer(s) on Period
Relates to #989
* adds layer menu support: Layer -> Center View on Selection
* relocate Center View on Selection to View -> Zoom to selected
* use the proper menu title
