Add chrome.bluetooth and chrome.bluetoothLowEnergy for iOS

I also create a peripheral testing app that simply simulate BLE heart rate sensor, and I will add more to simulate other things for more tests.
https://github.com/oahziur/ble-tests-helper

I removed `chrome.bluetooth.startDiscovery` and `chrome.bluetooth.stopDiscovery` for iOS because I found that low energy devices can be found without calling them (which conflict with: https://developer.chrome.com/apps/app_bluetooth#le-discovery) on ChromeOS.
These 5 lines are repeated a lot. Probably makes sense to create a helper. E.g.:

    - callAndClear:(void (^)(NSError*)*)callback

(or however the heck you declare a pointer to a block callback!)