Untested implementation of Task2

- This implementation searches for Controversial movies
  by calculating the sums of their minimal and maximal ratings,
  and comparing if they are >=n for n=100.
- I'm aware that I should probably have the keys being TextIntPair, rather than the values.
  I'm looking forward to change this, but it'll have to wait till tomorrow.
Bugfix in task2/ControversialReducer.java

- Type of input key was Text instead of IntWritable
Untested implementation of task4

- The sorting/grouping part is still expected to be broken.
- task4 consists of two jobs that need being run sequentially.