Multiple improvements to processing of inventory upload:
 * initialize required invoice fields
 * off-by-one row numbering (0-based -> 1-based)
 * error handling for queries
 * insert perl-undefined and zero-length string values as NULL database values
 * fixes to SQL queries
(grafted from 637caa20101f033677f19c8a368e99120319268b)

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extra : source : 637caa20101f033677f19c8a368e99120319268b
Make inventory upload work:
 * Remove hard-coded AR/AP account numbers
 * Allow use of specific upload UI based on type of upload
 * Add specific upload UI for inventory, including AR and AP accounts
(grafted from 8dde85694ed75ae5c7d25a635cb34a1cae537f8e)

--HG--
extra : source : 8dde85694ed75ae5c7d25a635cb34a1cae537f8e