* Add ExplicitContentFilter property to Guild

* re-order properties to match order listed on api docs

* re-order SystemChannelId to match api docs

* Implement ApplicationId in Guild model

* Add ExplicitContentFilter property to Guild

* re-order properties to match order listed on api docs

* re-order SystemChannelId to match api docs

* Implement ApplicationId in Guild model

* Improve xmldoc for IGuild ExplicitContentFilter

* Update xmldoc

* docs "Id" -> "ID"

* rename Test.GuildPermissions to a more general Test.Guilds

* Add ExplicitContentFilter to GuildProperties

* Add a test for ExplicitContentFilterLevel modification behavior

* Implement ModifyAsync behavior

* simplify ExplicitContentFilter test

* Add RestGuild ApplicationId inheritdoc

* Implement message Activity and Application model update

* RestMessage Application and Activity implementation

* add ToString to MessageApplication

* Add IconUrl property to MessageApplication

* clean up whitespace

* another excessive whitespace removal