Create index fix

[dantownsend]

Fixes #431

When creating indexes, the column names need to be quoted in case they have problematic names like 'order'.

[codecov-commenter]

Codecov Report

Merging #433 (2128a9c) into master (8500c81) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #433   +/-   ##
=======================================
  Coverage   90.84%   90.84%           
=======================================
  Files         103      103           
  Lines        6870     6870           
=======================================
  Hits         6241     6241           
  Misses        629      629           

Impacted Files	Coverage Δ
piccolo/table.py	95.54% <ø> (ø)
piccolo/query/methods/create_index.py	97.05% <100.00%> (ø)

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