Improve DashboardView Empty View

[ItsJakeMarcus]

This code adds a ContentUnavailableView to the DashboardView. Its purpose is to create a user friendly UI for when there are no maintenance jobs in the list.

• Closes IMPROVE - Empty DashboardView #286
• Adds UI to the previously blank DashboardView on the occasion there are no maintenance jobs in the list.

How I Tested

• Add a list of steps to show the functionality of your feature
  For example:
• Run the application
• On launch, the DashboardView will show a loading screen, and then the ContentUnavailableView
• You can add a maintenance task, which will replace the ContentUnavailableView, and delete them all, which will bring it back.

Notes

• N/A

Screenshot

[mikaelacaron]

Good work! Just a few comments of some things that need to be changed before it's merged

If you have any questions, you can comment directly on that thread, otherwise click the resolve button once you've addressed my comment. Once you fix everything, please click the re-review button

[mikaelacaron]

Great work on your first PR!! Thanks for contributing!

I fixed the tabbing because there was extra space above and below the ContentUnavailableView that didn't need to be there