Merge pull request #4 from ledgersmb/master

Merge Chris's fix for Cash/Payments
Fix LedgerSMB::App_State::User not being initialized correctly.
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
Correct typo.
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
Add missing questionmark to signal start of URL-query string.
Merge pull request #38 from ehuelsmann/master

Improve inventory upload & miscelaneous