zero prefixed house numbers

[missinglink]

following on from #162 this PR addresses some issues and omissions I discovered when updating the importers:

1. A house number of many zero (such as 00000) would return an empty string and error, this actually occurs in live data, we now squash it to 0.

2. The 'name' field(s) were not being updated. I thought through a few different options including updating all the importers directly and settled on this code which handles it fairly elegantly.

[missinglink]

diff --git a/test/data/expected.json b/test/data/expected.json
index 9cc6135..20841c2 100644
--- a/test/data/expected.json
+++ b/test/data/expected.json
@@ -184,13 +184,13 @@
     "_id": "openaddresses:address:input_file_1:f026cd5494a7e4f4",
     "data": {
       "name": {
-        "default": "00 Elm St"
+        "default": "0 Elm St"
       },
       "phrase": {
-        "default": "00 Elm St"
+        "default": "0 Elm St"
       },
       "address_parts": {
-        "number": "00",
+        "number": "0",
         "street": "Elm St"
       },
       "center_point": {
@@ -207,13 +207,13 @@
     "_id": "openaddresses:address:input_file_1:4509c0194f1efaca",
     "data": {
       "name": {
-        "default": "00300 Main St"
+        "default": "300 Main St"
       },
       "phrase": {
-        "default": "00300 Main St"
+        "default": "300 Main St"
       },
       "address_parts": {
-        "number": "00300",
+        "number": "300",
         "street": "Main St"
       },
       "center_point": {