Media server checking file content size
If the file is bigger than a given threshold, the upload should fail
- The previous media.sizelimit property was being used by DiskFileItemFactory
as sizeThreshold: http://commons.apache.org/proper/commons-fileupload/apidocs/org/apache/commons/fileupload/disk/DiskFileItemFactory.html#setSizeThreshold(int)
- Right now, the media server provides two types of content size checking:
1. The client can set a content-length field
2. If the provided content-lenght is smaller than the limit, but the actual size is bigger, the media server returns an error

Fixes #29
Checking if content-length field is null
Several code fixes
File content size limit tests