Silently fails to open non-utf8 files

[Ivo Anjo]

The attached file is iso8859-15 encoded, and it seems uberwriter expects utf-8 only.
That's not really a problem, but at currently uberwriter silently fails, just giving

WARNING:uberwriter: load_file() 'Error Reading File: UnicodeDecodeError('utf-8', b'\xe7\xe3\xe9\xe1\xf5', 0, 1, 'invalid continuation byte')'

on the shell, which is obviously very user-unfriendly.

The original file that triggered this issue was authored by a non-technical friend on notepad on windows (which in 2014 seems to still NOT default to utf-8...), and she was very confused by not getting any kind of feedback on why her file was not opening.