Increase maximum length for multi-line text prompts for properties

It could be argued that this is a bug (although not a very critical one!). Steps to reproduce:

• Create a text area.
• Add a multi-line property control with a string property.
• Paste >2MB of data into the textarea control.
• The data isn't entered into the Spotfire document property.

I think the problem is that Spotfire is attempting to send the value in a single request to the server and the request exceeds the maximum size that Tomcat will accept. I know this seems an odd use case, but I was attempting to build something in Spotfire that allows users to upload CSV files in their browser - this limitation means we can't upload files over a certain size.