Major code cleanup

This fixes jasperproject/jasper-client#123 and also fixes jasperproject/jasper-client#119. It partly resolves jasperproject/jasper-client#51.

You now should use "client.jasperpath"-module for all path related stuff (instead of hardcoding the strings). There's room for improvement (e.g. put the paths into a config file), but anyhow, this should do it for the moment.

Also, you really need to use the "tempfile"-module, which will create temporary files in the right location (and deletes them afterwards).

Last but not Least: I really don't get all this crazy sys.path-manipulation...what's the deal with that? I removed it for now.

I'll hope you can use these changes.

Fun fact: I did this to make it possible to create a ArchLinux PKGBUILD.
Well, it depends. Some platforms/OSes may not allow to open a file multiple times at one (in write mode). So if we do that, the code looks nice, but it will break platform-indepence.