Get and set wallpapers on GNOME in Linux

[nkprince007]

• Also changed error messages in GetWallpaper() and SetWallpaper()
• It works

[coveralls]

Coverage remained the same at 98.519% when pulling 531fb0810f4bafa7849d4f04b69cf8157dbd68c8 on get-set-wall-linux into 59ef05c5df7c9c71b34f6ab2827ee269d902690a on master.

[coveralls]

Coverage remained the same at 98.519% when pulling 86ddb09757d732ebe19323bfcf54a9215865323f on get-set-wall-linux into 5d4a6e517eeadb8f03e05e91c791b011f0d3e5ba on master.

[coveralls]

Coverage remained the same at 98.519% when pulling 3c3bdf7a20109691e7c446001238286c367f6f10 on get-set-wall-linux into 5d4a6e517eeadb8f03e05e91c791b011f0d3e5ba on master.

[nkprince007]

Can we rather have an editorconfig?

[Compro-Prasad]

I don't think we need it. Because go fmt is enough to do the stuff. I just added something so that Emacs users(if any and including me) could get the tab width of 4 spaces when opening a file in this project.

[nkprince007]

:P what about people using other text editors? EditorConfig unifies all of the needs.

[nkprince007]

also, I think we should rather take care of conditional builds rather than having two functions. Can you cherry pick and squash the commits together?

[Compro-Prasad]

I don't know how editorconfig will perform with Emacs because different languages, modes and buffers use different variables to set styling properties. Its better if we can try it out.

[nkprince007]

Please rebase your branch with master so that this PR can be merged. Also check for failing CI builds.

[coveralls]

Coverage remained the same at 98.675% when pulling 3ddfeae05eef14fc4a1da9575e3a6ff920056835 on get-set-wall-linux into f614cab3e09951a6ad87467bab4948ce44572262 on master.

[coveralls]

Coverage remained the same at 98.675% when pulling dcfe6d40496c22c60fc56406d36e445b47e84a5e on get-set-wall-linux into f614cab3e09951a6ad87467bab4948ce44572262 on master.

[Compro-Prasad]

Is the PR okay now?