improve discoverability of inspecting/editing connection attributes

[namdre]

Problem: People are not aware of the Inspect mode 'show connection' toggle Proposed solution: put additional buttons into connection mode because this is where people expect to find connection related things

• toggle button 'always show connections' (mirrors the functionality of the inspect mode toggle)
• toggle button 'inspect connections' (when active, left click on connection in connection mode switches to inspect mode and inspects that connection (default 'false')

[namdre]

Import because it's so easy to miss