Better error reporting and handling

[Tokeiito]

While testing does this supports custom servers, stumbled upon several errors like:

    control_points = int(comp.getApiClient().me()['gcl'])
KeyError: 'gcl'

    me = comp.getApiClient().me()['username']```

if there are problems with connection, wrong user name, wrong password or other, better error messaging might be helpful to debug and understand what is wrong with configuration.