Made relevant changes for adding background script

Created a background.js file that will run as a background script -
indicated it in the manifest.json and made functions in scrollpad.js to
call approporate methods of the background script
Added Options Page

Created options.html page for Options UI, options.js to save, load and
reset options. Reset options require communication with background
script, so made appropritate changes in background.js. Finally added
options page to manifest.json
make it compatible
merge background with master