Ability to align table elements

[uniomni]

In particular we need to be able to right justify numbers.
However, when doing something like

row = TableRow(['12', '3000', '5'],
                               col_align=['right', 'right', 'right'])
print Table(row)

or 

cell_1 = TableCell('12', align='right')
cell_2 = TableCell('3000', align='right')
cell_3 = TableCell('5', align='right')
row = TableRow([cell_1, cell_2, cell_3])
print Table(row)

results in the error message:

  File "/home/nielso/sandpit/inasafe-dev/impact_functions/tables.py", line 391, in __str__
    max_column_count = self.max_column_count()
  File "/home/nielso/sandpit/inasafe-dev/impact_functions/tables.py", line 324, in max_column_count
    for row in self.rows:
TypeError: 'TableRow' object is not iterable