Refactor/lazy provider

[bdmendes]

Closes #659

This PR:

• Removes the old behaviour of loading all app data upon startup and only does so the first time a Provider needs it. For that logic to work, a custom LazyConsumer is used to replace Consumer.
• Makes the last refresh time Provider-dependent (instead of global), saving it on the shared preferences instead of the db
• Makes the refresh page-based
• Allows caching the offline data for a while, avoiding multiple requests in a very close period of time
• Simplifies RequestDependantWidgetBuilder to make loading status more consistent

Please review this carefully as this changes the main flow of the app.

Review checklist

• Terms and conditions reflect the current change
• Contains enough appropriate tests
• If aimed at production, writes a new summary in whatsnew/whatsnew-pt-PT
• Properly adds an entry in changelog.md with the change
• If PR includes UI updates/additions, its description has screenshots
• Behavior is as expected
• Clean, well-structured code

[LuisDuarte1]

Congratulations! 🥳 This one is a tough one and you managed it super well 😃 with no visible regressions that I can test. I just have some concerns below related more to maintainability and knowing how some parts of the system works

[LuisDuarte1]

LGTM, good work! 🚀 🎉

[Sirze01]

The only thing I don't agree with is when using a non-persistent session the homepage loads with no widgets, not even the default ones (Is this intentional?).

Otherwise good job, a great refactor, both in size and quality.

[bdmendes]

@LuisDuarte1 @Sirze01 I have opted to always load from storage, even if the session is not persistent, to generalize the loading and avoid bugs like the one @Sirze01 found. To make sure data does not get loaded into storage when the session is not persistent, I suggest tackling #835 in another PR.

[Sirze01]

It's great now. Working as expected

[LuisDuarte1]

LGTM! nice catch 🎉