Implemented custom pointer icons for all drag and drop operations.
Removed ModelCacheSource.
Removed namespace prefixes from typenames for displaying to the user.

Fixes #389.
Fixed various PlugValueWidget setHighlighted() implementations.

They were all failing to call the base class implementation first.
Added blinking indication for plugs preventing the opening of a colour picker.

Fixes #185.
Improved (hopefully) icons used for drag and drop.
Fixed Shader node bindings to use DependencyNodeClass.
Fixed texture shader to work with GLSL version 120.
Merge pull request #390 from johnhaddon/modelCacheRemoval

Removed ModelCacheSource.
Merge pull request #391 from johnhaddon/typenamePrefixRemoval

Removed namespace prefixes from typenames for displaying to the user.
Merge pull request #392 from johnhaddon/nonEditableColorPlugs

Blinking colour widgets
Reverted non-gui ExecutableRender::execute() to block until the render is complete.

Not having this was preventing the test and screengrab apps working correctly.

Fixes #353.
Refactored Shader classes.

- Removed Shader::shader() and Shader::shaderHash() virtual methods, replacing them with Shader::parameterHash() and Shader::parameterValue() virtual methods. This simplifies the task of implementing derived classes.
- Made Shader::state() return a const value, making it possible to cache values in the future.
- Fixed hashing of RenderManShader coshader array parameters.

This refactoring should make it easier to implement the enabledPlug() and correspondingInput() stuff required by #327.
Fixed overzealous drag begin behaviour on LabelPlugValueWidget.
Fixed root cause of drags being started with no buttons down.
Fixed over-zealous NameLabel dragBegin.
Implemented enabling/disabling for shader nodes.

By default disabled shaders behave as if their output connections didn't exist. RenderMan shaders may change this by defining a "primaryInput" annotation nam
ing an input coshader parameter - this will be used to make the disabled shader act as a pass-through.

Fixes #327.
Merge pull request #386 from johnhaddon/dragDropPointers

Custom pointers for drag and drop operations
Merge pull request #395 from johnhaddon/disabledShaders

Enabling/disabling for shader nodes