Allow passing page options into phantomjs

This is an update to PR #21 (not trying to steal any credit here!) just wanted to make this long running feature request easier to merge with latest master and combine the good ideas of others.

Credit to @pconerly and @jakerella with improvements from @ssafejava .

Hoping someone from @gruntjs team (@cowboy or @jsoverson, et al? ;) can have a moment to look at this and let me know if there is feedback or this can be merged. Others have mentioned it's useful, and I found it helped with some jquery-ui tests as well (jquery/jquery-ui#1144)

**Merged in from ssafejava/grunt-lib-phantomjs@e356ada8c2b1e7c956886f344bb2102821b88961
(Essentially merged and squashed commits of #21 and #47 together)**