Embedded OpenSans Font and create Common Font Variables in DynamoModern.xml
Change current font to Embedded OpenSans for all UI control in DynamoView window

Conflicts:
	src/DynamoCore/UI/Views/DynamoView.xaml
New Dark Theme UI for all control such as Button, Textbox, Checkbox, Dropdown
Implemented PreferenceSettings

Settings that became persistent:
1) Show Console
2) Connector Type
3) Fullscreen Watch Mode

Test cases included
Improvement on UI Textbox Watermark behavior
Merge pull request #750 from l2obin/CherryPickEmbeddedFontFeature

Cherry pick features from ChocoButter to ChocoButterUI