structured: make string replacements case insensitive

[missinglink]

I noticed today that a /v1/search/structured query returned different results based on the casing of the unit number:

/v1/search/structured?address=kinkerstraat+175f

"parsed_text": [{
  "housenumber": "175f",
  "street": "kinkerstraat"
},

/v1/search/structured?address=kinkerstraat+175F

"parsed_text": [{
  "housenumber": "175f",
  "street": "kinkerstraat 175F"
},

This PR resolves the issue by converting some string replacement logic to be case-insensitive.

[missinglink]

I pushed a rebase which uses _.escapeRegExp(), because safety.