Refactored Web Package

MultiPartFormOutputStream removed
HttpBuilder adapted (lean version of MultiPartFormOutputStream)
Moved constants to Constants.java
Adapted calls in ConnectionWrapper
Refactored error message
Web package refactoring

changed access of HttpBuilder & FtpProgressInputStream to package
private
corrected typo
corrected locale warning
Moved constants

Constants moved back to HttpBuilder-class
Acceptance changes

changed constants to private
removed unnecessary method
removed redundant null initialization
Merge pull request #161 from Catrobat/RemoveMultipartformOutputStream

Remove multipartform output stream