Generate .desktop file for Gnome and other desktop environments.

[caiofaustino]

I got this idea from Android Studio/IntelliJ where they have a menu option to "Create Desktop entry..." and it generates a .desktop file for Gnome for example.

I created an entry for myself, but I didn't know where to get the icons at first. And I still don't know where the green icon for Testnet comes from. It would be convenient to have this option on bitcoin-qt as well.

[hebasto]

@caiofaustino

... And I still don't know where the green icon for Testnet comes from.

gui/src/qt/networkstyle.cpp

Line 21 in a426317

{"test", QAPP_APP_NAME_TESTNET, 70, 30},

It would be convenient to have this option on bitcoin-qt as well.

Concept ACK.

[hebasto]

@caiofaustino Mind testing #38?