Make error alerts less verbose, less technical and fewer

[podliashanyk]

Error handling in Howitz is currently not too user friendly:

• all errors lead to a separate error alert being shown
• each error alert requires manual action by user to close it (close all is possible only via manual page refresh)
• error alerts are very verbose (contain stack trace) and error messages are very technical (Python error names and descriptions are used)
• active bug [BUG]: Expand error alert operation is funky if error has no stack trace #57

While this error feedback is useful during alpha and beta releases, it is expected to be too annoying for full release.

Expected improvements:

• Handle errors that can be handled and do not prompt error alert if the problem is fixed
• Show only relevant error alerts to user, f.e. 4XX HTTP errors, server down/lost connection/timeout errors
• Make error alerts disappear if problem is fixed and show error alerts that require a manual close only on "unexpected error has occurred"

[podliashanyk]

Suggestion from @hmpf: if same error - show counter instead of new alert pop-up