bump version v0.20.0; fix output display (no longer clips text); seaborn style update; toolbar style compatibility in terminal mode

Add style for seaborn

Update stylefx.py

Fixed toolbar colors in the terminal app

output's collapse button size adjustment

fix cell output aligment

remove + 3 since it will overlay output print() text

The toolbar color when using the terminal app is set to body-bg (white) in jupyter's terminal.less. That rule has higher specificity than the one in the theme's notebook.less file and so takes precedence, making the toolbar white.

this resizes the collapse button so the output can be read properly

added flag to show kernel logo

Fix bug introduced in 9ba2240d

bump version v0.18.6; potential fix for encoding errors on python2, css/js defaults folder for overriding JT on reset