tccc scrapy export utf-8 json file and prettyjson.py

fix #9 

changelog

* move UnicodeJsonItemExporter to crawler_lib.misc
* add utils/prettyjson.py
* only tccc

example 

```
$ cd crawler/tccc
$ scrapy crawl councilors -o /tmp/test.json
$ python ../../utils/prettyjson.py /tmp/test.json 2
{
    "constituency": "第04選區",
    "contact_details": [
        {
            "label": "服務處地址",
................
    "term_end": {
        "date": "2014-12-25"
    },
    "term_start": "2010-12-25",
    "title": "議員"
}
```