[FLINK-1062] Type Extraction for Lambdas

I implemented the Type Extraction and updated all classes such that no Exception is thrown anymore when a user uses lambdas. I also added/updated several test cases to test the implementation.
We usually don't define simple "key/value" style entries like this (in three lines).
It is quite common for maven to have
```xml
<groupId>org.apache.maven.plugins</groupId>
```
and so on ..

Its minor, but we should treat our pom files with a bit more love (they are quite messy in some places)