Migrate to options page v2

[thom4parisot]

Reviewer:

Description:

options_ui is available since chrome@40 and gives a nicer modal layout to the options page.

More informations about the UI on https://developer.chrome.com/extensions/optionsV2

Steps to test this PR:

• install extension in Developer Mode
• open the extension Options via a right click on its icon or via the Manage Extensions menu
• witness it opens in a modal rather than in a new tab

Automated tests:

N/A (or having a JSON linter for the manifest.json file)

Reviewer Checklist:

• Ensure the PR solves the problem
• Review every line of code
• Ensure the PR does no harm by testing the changes thoroughly
• Get help if you're uncomfortable with any of the above!
• Determine if there are any quick wins that improve the implementation

PR Author Checklist:

• Get advice or leverage existing code
• Agree on technical approach with reviewer (if the changes are nuanced)
• Ensure that there is a testing strategy (and documented non-automated tests)
• Ensure there is a documented monitoring strategy (if necessary)
• Consider systems implications