TODO item action group

Currently, IntelliJ Platform doesn't seem to allow adding any actions directly into the TODO item action list.

Instead, I somewhat hacked it by adding my action into the `VersionControlGroup` that's being inserted into the TODO item's context menu.

Let's introduce this capability into the platform and rely on it instead of the current hack.

See the code near this line: https://github.com/ForNeVeR/Todosaurus/blob/7c8e5a52995745c4a93a2c44755d41556622ef09/src/main/resources/META-INF/plugin.xml#L14

Also, look for the number of this issue in the project code base.