Added basic DBSCAN script for clustering.

When supplied with list of coordinates for unique users, can pick out
major cities. Tested with welsh tweets, picks out Cardiff, Swansea,
Newport, Caerfyrddin, Caernarfon, Llandudno with ease. Tweaking picks up
Llanelli, Mold(?!) and London.

Currently need to cut out non-UK tweets when working with Welsh - DBSCAN
picks clusters out from background noise, and lack of worldwide Welsh tweets
creates odd 'background'.
Added major Welsh cities' coordinates.

Moved scripts relating to tweets and clustering to root folder - they
are general (as opposed to applicable only to Welsh tweet tracking).