[x] Added role support for tabs in main layout
By creating a permissions array inside each tab object with supported roles as strings inside.
Tabs will render if the chosen role exist inside its permissions array
[x] Welcome screen data is now from mocked server
Candidate and challenge info is now provided from server
[x] Added loading assets
Material UI CircularProgress loading animations included, shown by default the first second using setTimeout (it will be for now just for presentation, further it will change when connected to a real server)