Consistently named Commands

Suggested new names for easier auto-suggest:

```
:BookmarkToggle
:BookmarkAnnotate <TEXT>
:BookmarkNext
:BookmarkPrev
:BookmarkShowAll
:BookmarkClear
:BookmarkClearAll
:BookmarkSave <FILE_PATH>
:BookmarkLoad <FILE_PATH>
```

Keep the old names for backwards compatibility. They should be removed later on.
