Specify more precise times for avalanche problems

For problem types like Loose Wet, it can be possible to predict the times an avalanche can occur with more precision than is currently available with our system. Perhaps we could have a from-to times. It might be nice to have a nifty gui element to select the times with the daylight hours highlighted.

Start by tracing how the system currently represents and edits avalanche problem times, including the existing user interface and any persisted data. Define the from-to time behavior and daylight-hour selection requirements, then verify that forecasts can display and retain the more precise interval.

Written by the indexing model from the issue text.