asset class create/edit uniqueness

clean up the asset for changes to location, make unique external id per
asset class.
unit test fixes

Update unit tests after asset refactoring
AssetStatusHistory intro CRUD

Add, delete AJAX calls from Asset "show" page
cleanup

cleanup.  Still need direct table updates or refreshes
pushed from server.  Have controller return table elements
fix for assetStatus computation

new method for status calculator that takes Asset instance, fix asset
integ test, add depreciation calculator test
asset status history list

allow asset status history to be added and deleted without full page
refreshes via AJAX calls