Add logger widget for run_tardis():

[jaladh-singhal]

Add logger widget for run_tardis():

• Capture logger.info, .warn, etc. in a fixed-height textarea ipywidgets
• Make tabs for each log level
• Sort tabs by severity and don't show tab with empty content
• Make the logs show up colored
• Make convergence plots show once
• Make sure logs works on documentation website because widgets don't show up
• Test the widget with different combination of parameters and contexts in which it is used

[DeekshaMohanty]

3 is done (partially, I'm still unable to not display the tabs with empty content).
4 is done as well.