Replaced "NodeModel.OldValue" with "NodelModel.CachedValue"
Updated all relevant test cases to use "NodeModel.CachedValue"
Merge branch 'master' into PainKiller

Conflicts:
	src/DynamoCore/Models/NodeModel.cs
	src/DynamoRevit/VisualizationManager/VisualizationManagerRevit.cs
Migrate SunPath Direction
Refactor function initializer into the functiontable class
append the curveElement.curve node
Add type conversion to migration
Merge pull request #1579 from junmendoza/GlobalFuncTable_Initialize

Refactor function initializer into the functiontable class
Merge pull request #1580 from Zhengzi/Migration

append the curveElement.curve node
Merge pull request #1578 from ellensi/master

Migration
append element.geometry node to it
Merge pull request #1575 from Benglin/PainKiller

Optimized the way NodeModel handles its MirrorData
Merge pull request #1581 from Zhengzi/Migration

append element.geometry node to it