added require option and also ability to imbed screenshots in reports

[nikulkarni]

Two features added with this PR:

• Now one can attach screenshots to html report in all three themes
• Added require option so that one can specify step_definitions if they are not in default location under features directory like features/step_definitions

Check out the screenshots embedded in HTML below. FYI, JS to collapse/expand screenshots doesn't seem to work on the views below. However this has been thoroughly tested locally and everything works well.

http://htmlpreview.github.io/?https://github.com/nikulkarni/grunt-cucumberjs/blob/screenshot/report/cucumber_report_bootstrap.html

http://htmlpreview.github.io/?https://github.com/nikulkarni/grunt-cucumberjs/blob/screenshot/report/cucumber_report_simple.html

http://htmlpreview.github.io/?https://github.com/nikulkarni/grunt-cucumberjs/blob/screenshot/report/cucumber_report_foundation.html

[nikulkarni]

@mavdi Can you please take a look at this? Thanks!

[mavdi]

@nikulkarni looks good but can you please add some documentation as to how this can be done in the README?

[nikulkarni]

@mavdi I updated README with instructions

[mavdi]

@nikulkarni Thanks, merged and published.

[nikulkarni]

:+1: thanks