Select request by deviceId sent in header

[milovanderlinden]

We want to make it hard to guess request numbers, there for we need UUID's as keys instead of integers.

[milovanderlinden]

Related to codeforeurope/open311-android#54

[milovanderlinden]

Changed the title. From the android app, we are going to send a deviceId. This deviceId is also sent with the posting of reports. Should also be used to retrieve reports.