The destination configuration page did not previously support a textarea input as was supported on most other pages. The validation of string inputs was not being performed. This commit addresses both of those issues and corrects the validation expressions for the AWS and S3 destination plugins so that they continue to function. The SFTP destination plugin does not have any string validation. The Kubernetes plugin does not work at all as far as I can tell; there will be another PR in the coming days to address that.
* Adds the ability for destination plugins to be sub-classed from ExportDestination. These plugins have the extra option of specifying an export plugin before the destination receives the data. Closes#807.
* fixing tests
