Add overlay to queue lever pull jobs from linked building view

[pajawojciech]

How it works

• New overlay display button next to lever in 'Show linked buildings' tab.
• Button show lever status indicator: slash or backslash, representing current position of lever.
• Button adds / removes pull lever jobs
• Works fine even with more than one linked levers.

Click button

After click text changes to "Pulling" with yellow color, and job is queued. Now you can click again if you change your mind - it removes queued job.

Job assigned

When job is assigned text changes color to green:

Pulled

After pull text, color and indicator changes

When Unlink is enabled button moves to the left

What I tried

Instead of pull text i tried to set Open / opening / close / closing labels. For standard bridges it works fine, but for example retracting bridges or cages should have reversed operation naming, so I use 'Pull' text and lever position indicator

Issue

#3938

[chdoc]

I like the idea. However, I don't see any reason why this should be extending the buildingplan tool. In fact, I don't see why this couldn't be in scripts, for instance as part of the lever tool.

[pajawojciech]

I like the idea. However, I don't see any reason why this should be extending the buildingplan tool. In fact, I don't see why this couldn't be in scripts, for instance as part of the lever tool.

Thanks for review.
I made it this way because overlay reuses code from unlink_mechanisms.lua file (for example mech_iter, get_trigger_index and more). Also one new and two old overlays share the same screen space (and pull overlay checks whether unlink is enabled for good positioning), so splitting them would create duplicated code and fragille coordination.
Can scripts register overlay widgets?