Categorize activities

Hi,

in the `ActivityAttribute` attribute there is a `Traits` property (`Elsa.Metadata.ActivityTraits`).

I would like to use this to sort out `WorkflowExecutionLogRecord` entries. For example `If, Loop, Switch` don't interest the user, he just wants to see the actions (folder created, email sent, ...).

What do you think about adding `ControlFlow` and `ManualTrigger` (UserTask) in `ActivityTraits` and categorize the existing activities.

For me, it would be best if `ActivityTraits` is stored in `WorkflowExecutionLogRecord` as well. Then I could filter on it directly and the data doesn't have to be loaded from the database.