Finalise Linux installation

After the final `make` command as per linuxbuild.md instructs ([sort of anyway](https://github.com/forio/julia-studio/pull/236)), there is no Julia Studio program nor a julia-studio command to start the program.

I'm not sure if adding `qtbase` to the `PATH` variable is supposed to enable this, but it doesn't for me. Removing it just removes the `junit` command which isn't something needed anyway but I've left it there.

The code in this pull request makes a shell command `julia-studio` which accesses julia-studio/bin/julia-studio.sh, I'm not sure how you'd add the program to the Linux applications menu