MAGN-4255: Create resource file with images for BuiltIn Functions

# Preface
BuiltIn Functions is one of categories, that generates its' nodes directly in Dynamo.
# Solution
Added default assembly DynamoCore. In this assembly we will look for icons for such members like operators and builtin functions. Also added resource files(small and large).
# Before
![image](https://cloud.githubusercontent.com/assets/8158404/4149051/4482ea50-342f-11e4-88b1-b1e7048dd491.png)
# After
![image](https://cloud.githubusercontent.com/assets/8158404/4149034/1b0ea0d8-342f-11e4-9069-58d2e027b828.png)
# Note
Icons added just for not overloaded methods!
# Reviewers
@Benglin, please take a look.

Link to YouTrack:
[MAGN-4255 DUI: Create resource file with images for BuiltIn Functions](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4255)
Link to old PR: https://github.com/DynamoDS/Dynamo/pull/2329