translate tests to mocha

I "translated" all your tests to mocha (I hope you like it):
- split in server and client tests
- solution for the problem that a server has to run for client tests (done before,
  after functions)
- add destroy server to README
- add 3 devel dependencies (I really hope thats ok)
- add 3 commands:

```
npm run cover
npm run mocha
npm test
```
npm run cover generates nice html pages below: 

```
.../ndata/coverage/lcov-report/index.html
```
BTW: At the moment we got:
```
=============================== Coverage summary ===============================
Statements   : 57.18% ( 251/439 )
Branches     : 40.32% ( 75/186 )
Functions    : 49.12% ( 28/57 )
Lines        : 57.18% ( 251/439 )
================================================================================
```

Issue #11 remains