Unix: add qmake INSTALLS directives for packaging

[virtualtam]

Hi, and thanks for your work on IanniX!

This PR is a first step towards *NIX packaging: it adds qmake entries for a proper make install target to be generated.

I'm not sure however how to properly deploy and use static files -i.e. files that are to be deployed, yet not bundled as Qt resources:

• Examples and Patches should go resp. to $$PREFIX/share/iannix/Examples and $$PREFIX/share/iannix/Patches
• is it possible to dynamically set a path at compile time, so that IanniX looks for the resources at the right place?

  Content

Modifications:

• lower-case name for the built TARGET
• rename icon.png to iannix.png

Additions:

• desktop entry
• INSTALLS
  • application (TARGET)
  • application icon
  • desktop entry

Related topics:

• http://www.iannix.org/help/topic/linux-packages/
• http://www.iannix.org/help/topic/startup-config-under-linux/
• https://aur.archlinux.org/packages/iannix-git/

Resources:

• http://doc.qt.io/qt-4.8/qmake-environment-reference.html
• http://stackoverflow.com/questions/7106442/qt-project-files-and-prefix-variable
• http://standards.freedesktop.org/desktop-entry-spec/latest/
• http://standards.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html

[gjacquemin]

Thanks!