Fixing less @import paths in auth/base/tree.

These paths were problematic for --NotebookApp.use_less=True mode.
Indenting MathJax rendered equations in rendered_html divs.

This is designed to match the indentation level of MathJax equations
in output.
Compiling CSS for this branch.
Centering for tables/images/math in Markdown.
Adding 1em spacing above and below tables in rendered html.
Removing extra comment.
Removing page.less from base style.less.
Refactoring the center/left justify.
Adding this feature to whatsnew.
Fixing comments on equation justification.
Merge pull request #4154 from ellisonbg/mathstyle

Center LaTeX and figures in markdown