MAGN-4396: icons for overridden methods

# Preface
Overridden methods have the same names. In this case we can't just generate icon titles just from method name.
# Solution
Create additional method `ShortenParameterType` for generating icon titles. `ShortenParameterType` will be called, if it wasn't found any icon by default.
Also added test for this method.

## Note
I'm not sure, that I have created understandable variable names... But I tried, if you find these names strange, please, feel free to criticize it.

# Reviewers
@Benglin, please take a look.

Link to YouTrack:
[MAGN-4396 DUI: icons for overridden methods](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4396)
The following code needs to be updated to this for better readability:

    "cs
    var name = GetResourceName(ResourceType.SmallIcon, false);
    BitmapImage icon = GetIcon(name + Dynamo.UI.Configurations.SmallIconPostfix);
    if (icon == null)
    {
        // Get dis-ambiguous resource name and try again.
        name = GetResourceName(ResourceType.SmallIcon, true);
        icon = GetIcon(name + Dynamo.UI.Configurations.SmallIconPostfix);
    }

    return icon;
    "