Add a USB device info viewer than demos the USB device picker.

This app displays information about any device available to Chrome. The
new chrome.usb.getUserSelectedDevices API is used to request permission
for arbitrary devices.
Move the USB device info app under the samples directory and add README.
Updated README.md to include screenshot and added icon.

Also fixed some small nits.
Merge pull request #330 from reillyeon/device-info

Add a USB device info viewer than demos the USB device picker.
Merge pull request #332 from samthor/master

Add custom HTML/CSS titlebar demo
usb_device-info: Handle the case of a device being selected again.

If the user selects a device that the app has already been given permission
for then this patch moves the selection back to that device instead of adding
a duplicate entry to its internal list.
Merge pull request #333 from reillyeon/device-info

usb_device-info: Handle the case of a device being selected again.
Don't disconnect same device of GATT services
Merge pull request #334 from oahziur/ble

 bluetooth-samples_heart-rate-sensor: Don't disconnect same device of GATT services
bluetooth-samples_battery-service: Able to connect devices inside the App
bluetooth-samples_battery-service: Add bluetooth discovery toggle
bluetooth-samples_heart-rate-sensor: Add bluetooth discovery toggle
bluetooth-samples_device-info: Add bluetooth discovery toggle
bluetooth-samples: simplify discovery callback handler
Removed unmanaged in-app-purchases sample apps (x2). Added managed-in-app-purchases sample app. Updated README.
Fixed README link to in-app-payments feature.
Merge pull request #339 from jakeleichtling/master

Remove unmanaged IAP samples and add managed IAP sample app
Fix link to managed in-app payments API.

The Markdown URL syntax was flipped.
Merge pull request #337 from oahziur/ble

Add discovery toggle button and connect devices in apps for bluetooth-samples