Lock node state should conform to UX standards

[ffxsam]

For icon buttons, typically they work like this:

• Icon reflects the current state
• Tooltip explains what happens if clicked

The lock button satisfies the 2nd point, but not the first. I would recommend either:

• making the lock icon simply turn blue when the node is locked
• flipping the icon states (opened lock = node is not locked; closed lock = node is locked)

[Calinou]

• making the lock icon simply turn blue when the node is locked
• flipping the icon states (opened lock = node is not locked; closed lock = node is locked)

I think we can do both: flip the icon state and make the icon blue when locked.

[ffxsam]

Sounds good! I wish I could help with this, but I don't know C++.