[Polish] TripPlanForm: Make pressing enter while inside a SearchBox do things

[pingzing]

Pressing enter while inside any of the search boxes on the TripPlan page should do the following:

• If the Plan button is enabled, trigger a plan for the current input.
• If not, move to the next empty box.

[pingzing]

Kinda works. Needs polish.

Problem: Focus returns to the searchbox after planning begins, and the popup is still visible.

Possible solutions: Disable the searchboxes, change the searchbox logic to not always show the popup on gaining focus.

Either way, pushing it back to 1.2. It's good enough for now.