Add mod icons to create unit trees

[mharis001]

When merged this pull request will:

• title, Close Interface Symbol #207

[Kexanone]

Looks fine, but changing the setting should trigger reloading the module tree.

[mharis001]

ZEN is sort of split on that right now. Some settings reload the display automatically (e.g. faction filter) while others apply once the display is manually reloaded (e.g. the similar group icons setting). I guess if we change it here, the behaviour should be made consistent across all features.

[Kexanone]

ZEN is sort of split on that right now. Some settings reload the display automatically (e.g. faction filter) while others apply once the display is manually reloaded (e.g. the similar group icons setting). I guess if we change it here, the behaviour should be made consistent across all features.

Agreed, we should have a dedicated PR for that. In fact I was about to make the same comment for the placement preview, but thought it was out of scope for that PR.