[UI Improvement] Improved patch cord selection, modification, and deletion

[gilbertohasnofb]

Patch cords are a bit tricky to interact with, particularly when multiple cords go from or into a node. Suggestion for improved patch cords:

1. click on patch cord to select (potentially making it in accent colour)
2. Control and click to select multiple cords
3. delete and/or backspace key to delete all selected cord
4. once selected, dragging from a node should affect that specifically selected patch cord(s)
5. the dark coloured cords for frequency domain objects are difficult to see and won't work if the suggestion 1 of accent colours is used. Here is a suggestion of how it could look like:

(accent colour could be louder than the image above but consistent with dropdown menu choise if #33 gets implemented)

[j-p-higgins]

#94 for more

In short, I would like to implement this but it requires overriding the default behaviour in Godot and rewriting cable creation from scratch. I will look to do this in future but this won't be implemented until later in the development process as it will be a considerable amount of work and for now I am focusing on getting audio processing implemented first.

[j-p-higgins]

Turns out there were some undocumented functions in Godot that have now been documented so this has been implemented, will be in the next update.

What is implemented:

• Click to select and highlight a cable (highlight is a brighter version of chosen background colour)
• Shift+Click to select multiple cables
• Clicking anywhere else unselects cables
• Delete/Backspace remove any selected cables
• Double clicking on a cable removes the cable
• High contrast mode in settings changes cable highlight to opposite colour to the background with boosted saturation