Features suggestion for user convenience

[hvdinh16]

• Add 'save as image' function to ipython escher like 'save as svg' on escher.github.io
• Save settings like how on MS office you can save templates/themes.
• Fold change conparison doesn't work on non-positive values and display as 'no data'

[zakandrewking]

Moved to Escher issues:

https://github.com/zakandrewking/escher/issues/155 https://github.com/zakandrewking/escher/issues/153 https://github.com/zakandrewking/escher/issues/127