Added right-click context menu

[saiflakhani]

I've theoretically been able to add a context menu.

You can now highlight a word and search with spot.

Current issues:

• ~~It simply opens the popup, doesn't really search~~ Search functionality added in 6fd092f
• Cannot open the actual popup. Prohibited by chrome
• Please refer https://stackoverflow.com/questions/13783500/context-menus-in-chrome-extensions

[saiflakhani]

Ping.

[schezfaz]

Ping.

Apologies haha, busy week at work!