試著實作 freedesktop.org desktop entry

參考了 freedesktop.org 的
[Desktop Entry Specification](http://standards.freedesktop.org/desktop-
entry-spec/desktop-entry-spec-1.1.html)
跟
[Desktop Menu Specification](http://standards.freedesktop.org/menu-spec
/menu-spec-1.1.html)
實作了 desktop entry

注意這個版本假定軟體安裝在 /opt/moedict-desktop 寫死了主程式路徑。

Signed-off-by: Ｖ字龍(Vdragon) <Vdragon.Taiwan@gmail.com>
Merge pull request #13 from Vdragon/implement-desktop-entry

試著實作 freedesktop.org desktop entry