Convert id to sting before querying

We store id as an alphanumeric as some lims use non integer identifiers.
However, Sequencescape currently generates messages with integer ids
as expected by the existing warehouse. While MySQl still returns the
correct records, it suffers a significant performance hit and we
can eliminate this by coercing our id before hand.
Merge pull request #5 from JamesGlover/next_release

Convert id to sting before querying