Add IE 11 and ES 5 support

• Fixed Promise issues due to incorrect ES 6 transpilation setting with TypeScript

Add backlog multi-select option

• Allow users to select multiple work items from the backlog and move all on the board
• Prevent users from using the context menu from the board
• README and overview updates

Add Doing/Done option

• Added Doing/Done option
• Update image for README

Initial release to VSTS Marketplace

Initial release.