Fix the importer upload. Fixes #1312.

A majority of this commit was ported over from MapStory and fixes the importer functionality that broke when we migrated to Geoserver 2.4, to my knowledge this will not be backwards compatible with Geoserver 2.3.  Thanks to @ischneider for helping with this.

**GIS Data tests:**
- [x] san_andres_y_providencia_administrative
- [x] san_andres_y_providencia_coastline
- [x] san_andres_y_providencia_highway
- [ ] san_andres_y_providencia_location -> **Failed from Importer gui import as well**
- [x] san_andres_y_providencia_natural
- [x] san_andres_y_providencia_poi
- [x] san_andres_y_providencia_water
- [x] single_point
- [x] relief_san_andres.tif
- [x] test_grid.tif

**Other Tests:**
- [x] KML import
- [x] Import with metadata
- [x] Vector imports with an SLD

**Notes:**
* This PR removes the geonode/geoserver/upload package in favor of using gsimporter (https://github.com/boundlessgeo/gsimporter).  Unfortunately, gsimporter is the only dependency we currently have that is not in PyPI which required me to switch to a requirements file during installation.

* This requires the gs-importer .jar files which are built with this modification to the geoserver-geonode-ext .pom file: https://github.com/garnertb/geoserver-geonode-ext/commit/a5740460a0842160819aa52d1c94a1ab878f8b5b.