tags ui improvements + tags synonyms

relevant issue: #124

1. improved tags ui:
    * added autocomplete
    * more intuitive interface
    * also, some refactoring of the code:
        * move tagging code to common template to prevent code duplication
    * affects:
        * tags api (tastypie)
        * committee meeting detail
        * vote detail
        * bill detail

2. Add support for tag synonyms:
    * Added a new model TagSynonym with 2 fields:
        * tag - the proper tag
        * synonym_tag - the synonym tag (should be redirected to the proper tag)
    * Added a management command that loads synonyms + deletes tags according to csv file
        * ./manage.py process_tags_file
        * it takes the data from data/tags.csv which is included - based on https://docs.google.com/a/uumpa.com/spreadsheet/ccc?key=0AiwMXCvG-BCwdGRIbENhblAydzJYcTFGTXRUUWFEakE#gid=0
        * by default does dry-run so you can check what it's going to do
        * to run for real add --no-dry-run
        * optional parameter --hebrev - might help in displaying the hebrew properly in terminal
    * added support in the tags autocomplete that displays tags synonyms in square brackets
        * when selecting a tag synonym it automatically saves the proper tag