Update cell styling, added conflict source class

render's neighborConflict method now assigns a class to identify the
source of the conflict - these cells receive special styling to make it
easier for the user to locate and correct the conflict.

Updates to styles include:
* greying out user input and disabling hover if selected cell value is
  locked
* changed cascade for various cell stylings, to ensure visability of
  when multiple class apply (e.g. selected and conflict-source).
* added 'noselect' class to body, should prevent accidental text
  selection when trying to click on a cell.