Ide 1.5.x linuxstuff and manpage

Here's some linux-related stuff (icons, .desktop file and mime xml file), based on #1639. The actual files are taken from the Debian package, though the .desktop file was changed a bit to resemble the file from #1639 more. The permission-checking script from #1639 is not included, because it seems to me that that is potentially quite distribution-specific (the Debian version is already different from the version in #1639).

Additionally, this adds a manpage as discussed in https://github.com/arduino/Arduino/pull/1639#issuecomment-29791545. The manpage can be viewed directly through github: https://github.com/matthijskooijman/Arduino/blob/ide-1.5.x-linuxstuff/build/shared/manpage.adoc