Clarify Data migrations using CSV

[neilt]

Explain how to do a partial migration.

There exists imports in the menu system for:

1. AR -> Import Batch
2. AP -> Import Batch
3. Goods and Services ->
   • Import -> Goods
   • Import -> Services
   • Import -> Overhead
   • Import -> Inventory
4. Fixed Assets -> Assets -> Import
5. Time Cards -> Import
6. General Journal ->
   • Import (Transaction)
   • Import Batch (Transactions)
   • Import Chart (CoA)

Make sure any Integration text improvements incorporates SQL-Ledger 2.8 migration text from the Wiki.