change color of msg on profile page

[sjanssen2]

When changing the user profile, the user gets feedback after he/she hits Save Edits. However, this msg is always red, even though it signals success, like here:

I suggest to use darkgreen by default:

and only change to red (through jinja code in the template) when the msg starts with ERROR:

[coveralls]

coverage: 92.85%. remained the same
when pulling d192195 on jlab:more_positive_color_for_success
into 1ffd9a0 on qiita-spots:dev.