Collaboration analysis with Features.

This pull request basically adds support for collaboration analysis with features instead of functions.
The analysis can be enabled with a new parameter "--collaboration", which can have the 3 values `function`, `feature_file` and `feature`

### `function`

Everything should be as it was before

### `feature_file`

Uses the same analysis logic as `function` but with `#ifdef` borders instead of functions.

### `feature`

> (SUM(MIN(line-changes of author1 on feature, line-changes of author2 on feature) FOR feature IN features))

This is basically the formula we use for measuring the collaboration strength between two authors between two releases.
This is done pretty straightforward by first filtering for interesting lines, then summing up the number of lines every author worked on a feature and then calculating the above sum.

Additionally I fixed some typos and updated nodejs. There are also Unit Tests for the parser of the cppstats outpuf file!

Some more details:
- When features are used we generate only the feature information ( codeface/VCS.py) and not the function-lines information. This could lead to problems when initially feature analysis is used and then (with the cache already build) one switches to function analysis.
- The code is a bit more general then the function analysis (it's a bit like nested functions) so sometimes the function code could use the new code (but I did not touch it currently)
- The new FileDict class (in codeface/fileCommit.py) could be used by the function analysis as well.
- Unit tests cover only the parsing code (which parses the output of cppstats). As some things are very deeply integrated into each other it is rather difficult to write tests for the other parts.
- As indicated by the comments (https://github.com/siemens/codeface/pull/6/files#diff-a5b05016ad1fb851d4da2276d9bce0f3R1175) on those lines: The cppstats dependency has to be handled properly. NOTE: this does not hurt as much as it sounds because the code only runs when features are enabled.