[Feature] Modify guild features

[Misha-133]

This PR adds support for modifying guild features & adds a few missing ones.

Changes

• add missing guild features
• add GuildFeatures json writer
• add GuildFeature property to GuildProperties

[csmir]

Would it not be wise to check the mutable features, to protect the developer from editing before unavailable ones get sent to discord? Maybe I read over this check, but I do not see it anywhere.

[Misha-133]

Would it not be wise to check the mutable features, to protect the developer from editing before unavailable ones get sent to discord? Maybe I read over this check, but I do not see it anywhere.

Discord ignores immutable features
is this kind of validation needed in this case?

[csmir]

Just a comment now is fine then, I will merge it

.