Solve #47: Use own Serializer/Deserializer for HTTP-Headers

Instead of Json we use a combination of string-concatination and UrlEncode.
For example a Map or TPIC with this content:
```java
final Map<String, String> context = new HashMap<String, String>();
context.put("Sven", "lovesTracEE");
context.put("Asterix says", "§$%&@/(");
```
is rendered to:
`Asterix+says=%C2%A7%24%25%26%40%2F%28,Sven=lovesTracEE`
The full TracEE-Header:
`TPIC: Asterix+says=%C2%A7%24%25%26%40%2F%28,Sven=lovesTracEE`