Upload history implementation. Enable value repeater to modify raw incoming data, to allow the values repeated down a data sheet to be stored in upload history.

Remove declared assert_true method, while only new php versions support asserts with messages, having the line number of the assert is more useful than the message (previously I was directing to a method that would display the message and always call a failing assert, but this requires a backtrace to find the actual calling location and is more hassle than it's worth)

Removed extra addition to error message in value processor, will just be expecting the raw error message pass up from below.