Reworked images for Message Log w/ added bonus 'Empty' Group icon

[GaryElshaw]

I was never particularly happy with the last lot of images i created, particularly the outer edges, so an update. I've also included White and Grey icon sets for any future project needs.

With #3065 a new circular 'Empty' icon was needed for Group.

[GaryElshaw]

@mikedld Mike, could you give some TLC to TC please?

[Coeur]

This PR is, presently, a combination of two changes:

1. GroupsNoneTemplate.png, which is the empty group icon;
2. *DotFlat.png, which are the message logs icons (which users rarely visit).

One issue from the usage of .png files is that it's not ideal for supporting both light mode and dark mode.
Considering the uniform content of those icons, I feel we can simply render them programmatically.

[GaryElshaw]

Sheesh Antoine, thanks for minimising my contributions :-(

[Coeur]

Hi @GaryElshaw
Thanks to you, I'm discovering features and ways to improve them.
I'll give a try to the icons generation.

[GaryElshaw]

@Coeur I totally agree with you that this would be great if it was done in code, especially for the OS versions with Light and Dark options.

I don't know what is currently possible for 4.0, but this is high on my feature list, and it seems i'm not alone after looking in the forums. In the interim, i have a local branch that alters a bunch of source files to increase font sizes. #1676

Which raises a separate discussion i've wanted to have with contributors and maintainers alike for a while, because i have too much time on my hands...
#3089