Provide version for About dialog on Mac

[gitting]

Mac apps usually provide versions when asked About <app>. Currently paisa doesn't provide that as in:

It would be good to have that.

[ananthakumaran]

Added to master, will be available from next release.

[avinashkanaujiya]

Same for linux, would be nice.

[ananthakumaran]

I have added a new about page https://demo.paisa.fyi/more/about.