Configuration parameter for data update strategy

[orontee]

Context

I often launch the application many successive time and I am annoyed by it fetching new data at evey startup.

Analysis

Add configuration parameter to select update strategy:

• only manually,
• hourly when obsolete (thus can be skipped at startup if restored state is recent)
• hourly since application startup (current behavior, will be the default strategy).

[orontee]

Implementation ready, testing.

[orontee]

Not clear whether all that stuff related to periodic data update is really needed. Let's keep things simple for now. I am closing this but let's keep the code ready.

I changed my mind after first experiments. The UI should not mention the hourly refresh which is confusing and not useless I guess, but being able to choose the refresh strategy at startup is nice. Landed on main branch.