Enhance Windows installer

This installer adds the following:

- adds icons to sclang (cube) and scide (circle)
- registers file-types in windows (and adds the cube-icon to them)
- registers uninstaller in Add-/Remove programs
- creates startmenu item
- removes everything on uninstall (hopefully ;))
- simplifies the nsis-script (and comments out everything related to gedit)
- installs the supernova executable to the main application-folder on Windows
- brands the installer with sc-logo and reintroduces standard texts

Comments welcome, be mild, I am new to this ;) It is basically copy-paste coding.