Refactor Request Dependent Widget

[bdmendes]

Show a more descriptive error message on RequestDependentWidgetBuilder.

[bdmendes]

@thePeras One more thing to consider is the case when there is local content available (and so the widget shows it) and meanwhile the app fetches new info, without visual feedback (no spinning circle since there was content), and new content 'magically' appears. We can improve on this, not hiding the spinning circle ever while fetching, showing the info at the same time.
An example: the app shows 'No exams scheduled' from the last record in the database, and new exams magically appear after fetching since they were scheduled recently by the faculty.

[thePeras]

Try not to use helper functions

[bdmendes]

@thePeras was this done?

[bdmendes]

Handled in #823