Update desktop files (#1263)

* Rename files to freedesktop standarts

* Add application icons

qt/i2pd_qt/data/website.i2pd.i2pd.appdata.xml

@@ -1,7 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!-- Copyright 2018 Viktor Villainov <supervillain@riseup.net> -->
 <component type="desktop">
-  <id>i2pd.desktop</id>
+  <id>website.i2pd.i2pd</id>
+  <launchable type="desktop-id">website.i2pd.i2pd.desktop</launchable>
   <metadata_license>CC0-1.0</metadata_license>
   <project_license>BSD 3-Clause</project_license>
   <name>i2pd</name>

qt/i2pd_qt/data/website.i2pd.i2pd.desktop

@@ -3,7 +3,7 @@ Categories=Network;P2P;Qt;
 Exec=i2pd_qt
 GenericName=Invisible Internet
 Comment=A universal anonymous network layer
-Icon=i2pd
+Icon=website.i2pd.i2pd
 Name=i2pd
 Terminal=false
 Type=Application