No queries header presented for cases "Create" - "Query" members available

#### Purpose

In cases when we have just "Create" and "Query" members "Query" member isn't shown.

#### Modifications

Making `DisplayModeToTextDecorationsConverter` as `MultiConverter` too handle situations when we have only header (`Query` or `Actions`).

#### Additional references

[MAGN-5394](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5394).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.
I'd recommend the following restructuring of this ```if (hasCreateMembers)``` clause (so that it is easier to reason about the code intents):

```csharp
if (hasCreateMembers)
{
    if (hasActionMembers && hasQueryMembers)
    {
        // If both 'Action' and 'Query' are available...
        castedDataContext.IsSecondaryHeaderRightVisible = true;
    }
    else
    {
        // Not both 'Action' and 'Query' are available, we 
        // may just be having either one of them, or none.
        
        if (hasActionMembers) // Only 'Action' members present.
        {
            // ...
        }
        else if (hasQueryMembers) // Only 'Query' members present.
        {
            // ...
        }
    }
}
```