Workfile Templates: Load Source placeholder in Sources + transfer connections to loaded products

[BigRoy]

Changelog Description

• Match graph position for loaded products to the placeholder node (for Load placeholders like load matteshapes or trackpoints)
• Create "Load Source" placeholder in project sources instead of as node in graph to allow much better placeholder behavior where the source can be re-used in graph, accordingly.
• Transfer connections from the placeholder nodes to the loaded items.

Additional review information

Fixes draft implementation of workfile templates.

Note: When building a template where a single placeholder loads multiple products then on build the multiple entries will appear on top of each other in the graph with only the last loaded product to receive get the outputs transferred because the destinations can only be connected to ONE of the loader items.

Note that "Create" placeholders have been untested still and likely won't work - so please test only Load Placeholders

Testing notes:

1. Create a workfile template file
2. Updating placeholders (incl "Load Source" load placeholder) should work when selecting in the "Sources" panel
3. Build the workfile template.

Template "Load Placeholders" should work.