Improve handling of errors during source-loading #17
Description
Some sources may fail to load temporarily. Currently the error messages are very intrusive and don't properly disappear (and can't even be dismissed).
Making the errors much smaller and dismissable would improve the overall UX.
Example, a tag-like display near the top toolbar showing the status for each source. A progressbar is less useful as the items are loaded asynchronously. This could be visible all the time, or fade-out after the loading process finished.