Change toGlobalId ID parameter to be either string or number

[intellix]

Closes #218

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[coveralls]

Coverage remained the same at 99.46% when pulling 11fb043 on intellix:patch-1 into da2801a on graphql:master.

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[sibelius]

it makes sense

[kassens]

I'm pretty out of the loop of this code, but fromGlobald is the opposite and returns a string. Might be nice to keep this a bijection?