UI/connectivity warning

[jcovaa]

Closes #528
//

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

[jcovaa]

Some prints of the warning.

[thePeras]

I like the design. If the pharse was rephase to "Attention: No internet connection" would be better than demanding an action from the user. The user may be checking his next class, local data will be sufficient and no internet connection is required.

[jcovaa]

I liked more this design but it doesn't fit with some pages.
Edit: changed the phrase to "Attention: No internet connection" and "Atenção: Sem conexão à internet"

[jcovaa]

Some more design ideas

OR

[thePeras]

I like a lot the option without background and red text on light and white on dark.

[thePeras]

One last request:
Don't upload an asset image to use as an icon. Import from the icon package Uni is using

[thePeras]

Well done guys!

Don't forget to make the actions go green!

[vitormpp]

To make the position of the ConnectivityWarning fixed, move it to the getTopNavBar method in GeneralPageViewState (however, note that the layout of the pages may change during the redesign).

[jcovaa]

Following the conversation we had, I tried to change the _createTopWodgets method in the top_navigation_bar.dart class but there are 2 problems. The first is that the home page uses a getHeader method that creates the tittle differently from the other pages (the warning appears above instead of below the tittle). The second problem is that the size of the AppBar isnt dynamically changed when the warning is displayed, so it seems cut out. Do I have to increase its size or its my implementation that isnt correct?