Priority Signs: Interaction model is whack

[originalfoo]

I've been working on docs for priority signs feature, and realised the interaction model of that feature is not consistent with other junction-related tools.

In particular, with a junction selected (that has a sign added to at least one of its roads), I should be able to right-click to deselect that junction.

When a junction is deselected, the red X button in the middle should be hidden. This will reduce risk of accidental settings deletions (useful if you have shit mouse, like I do, or a disability), especially when working with close-proximity junctions.

Also, due to the selection/deselection weirdness, the red-X button, considering where it's placed, can be mistaken for a "close" button by new users. While I love the simplicity of the holy shit, house down the road from me has installed a wind turbine! Uhm, I love the simplicity of the red X button, but maybe having a trash can icon would be better?

Suggestions:

• Change icon on red button to a trash can (I'll submit a PR for review)
  • Does that icon get re-used for "Clear vehicle" button on vehicle info panels?
  • A trash icon would make more sense there too ;)
• Trash button should only appear for currently selected junction
• Right-click to deselect junction
• Blue circle appears in any un-selected junction when mouse hovers, allowing selection of that junction
• Shortcut: Click sign icon of any previously customised junction to cycle that sign + select that junction

Note: If Eraser tool is implemented at later date (see #38 for brief info), it's possible the trash button could be ditched to further simplify on-screen UI.

[originalfoo]

assigning to self to do the trash icon

[originalfoo]

Proposal for new 'delete' icon (it was previously just a white "X") - let me know if it's OK and I'll send a PR. It's bit darker than old one to give more contrast when it scales down for use on vehicle info panels.

[krzychu124]

Looks good 😉

[krzychu124]

I've made quick test and it looks really good

[kianzarrin]

related to #541

[originalfoo]

There have been loads of good improvements to the priority signs stuff, but the user interaction for editing is still a bit weird because there are two interaction models depending on whether a junction is already customised or not:

1. If not yet customised, user has to select the node first
2. If already customised, user can't select the node, they can only edit/delete

That, in a nutshell, is why it is clunky to use.

There should be only one interaction model, regardless of whether the junction is customised or not.

I think, in particular, user should always have to "select junction" to make changes. And to revert to default it should be Delete | Backspace like other tools (ie, get rid of the bin icon).

In OP I pondered user being able to click overlay icon to cycle the sign + go in to junction edit mode. However, that would be weird too (imagine tryying to make that viable for all the other tools that show only "changes from default" icons).

[kianzarrin]

I mark this as dependent on #863 because there are some fixes in #863.
we should not work on this until #863 is resolved.

[kvakvs]

We can plan this after UI tools are modified
For today i have:

• speed limits
• vehicle restrictions
• timed traffic lights
• and then we can revisit this, add a nice clean state transition Select → Edit → Select or Edit again