Added features and fixed bugs

1 - CerebralCortex supports file-system as data-storage layer. This could be useful if you are running it on single node
2 - get_stream returns local time of a participant. Datatime object would have (-/+) of timezone hours. (https://md2korg.atlassian.net/browse/CC-483). If you set localtime=False, then please set the same localtime=False in save_stream (API change)
3 - Fixed Datetime object serialization while using json.dumps
4 - Fixed bug related to remove duplicates on storing data in HDFS (save_stream)
5 - Moved hdfs related methods to stream_handler module (improvement
6 - Set localtime=False (default value)
7 - Manually opening/closing files to avoid any "FileAlreadyColsed" errors
8 - Added system level test-cases
9 - Fixed a critical bug (https://md2korg.atlassian.net/browse/CC-536)
10 - Added caching feature to cache GPS and mobile app cat. data