BUG: CR and LF replaced in URL when uploading extensions

CMake string variables can contain new lines [1][2]. The Slicer extension
mechanism uses string CMake to create extension description files and to
create the URL containing meta-data and the package file name to upload
extensions to the Midas server. New lines need to be handled correctly,
otherwise the user will receive a message that the Midas server did not
accept the submission of the extension. Carriage Return (CR) and
Line Feed (LF) need to be replace by equivalent URL-encoding characters.

[1] http://slicer-devel.65872.n3.nabble.com/Problem-with-the-factory-not-uploading-some-extensions-td4035069.html
[2] https://github.com/Slicer/ExtensionsIndex/pull/1112#issuecomment-145706433

From: Francois Budin <fbudin@unc.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24600 3bd1e089-480b-0410-8dfb-8563597acbee