Add Revit specific icons to DynamoRevit repository

#### Purpose

Revit specific icons should be situated in DynamoRevit repository.

#### Modifications

Created project `DynamoRevitIcons` similarly to Dynamo's project `DynamoIcons`.

#### Additional references

Add part of task [MAGN-5672](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5672) DUI: Move Revit specific icons to DynamoRevit project.

#### Reviewers

@Benglin, please, take a look.