Support for Slovenian localisation

[Prome88]

I'll add it. Can someone (@krzemin / @MichalKrasowski) confim (based on the commits for IT lang support) if I got all the files which need to be changed / added for new language:

• doc\main\si\qnapi.1 [ADD]
• doc\main\si\qnapi.1.gz [ADD]
• doc\qnapi-download.desktop [EDIT]
• doc\qnapi-scan.desktop [EDIT]
• doc\qnapi.desktop [EDIT]
• gui\res\langs\si.png [ADD]
• gui\ui\frmoptions.ui [EDIT]
• qnapi.pro [EDIT]
• translations\qnapi_si.qm [ADD]
• translations\qnapi_si.ts [ADD]

[krzemin]

@Prome88 yes, it seems that's all.