Add package `htmlize`

To highlight source code in org-reveal src block, this package is
required. It is included in org-mode contrib, but not in GNU ELPA.
Revert "Enable `global-hl-line-mode'"

This reverts commit 9bc5db0cf81842e70007872e7e9dac65494dc6d9.

If the text has light background and dark Foreground such as those
highlighted by `highlight-symbol`, it cannot be seen easily on current
line.
Disable `global-whitespace-mode'

whitespace-mode does not work well with popup.el
http://stackoverflow.com/q/12965814