Added HSV readout for pixel below mouse in image viewer.

Fixes #576.
Fixed problems packaging GafferOSL for release.
Simplified public build using tarball with all dependencies.
Allowed PathFilter paths plug to receive inputs.

I had disallowed it because in theory you could connect an expression into it where the expression depended on scene:path, and that would mean that ancestor/descendant queries could fail. However this prevented lots of sensible use cases including plug promotion - it's preferable to allow the sensible use cases, as the problematic case is really obscure and unlikely to occur in practice

When we start implementing AttributeFilters and the like, we might add a mechanism whereby filters can specify that they can't support efficient ancestor/descendant queries, and when we detect an input from a ComputeNode the PathFilter could perhaps disable those queries. But that might be overthinking it again too...
Renamed CheckBox to BoolWidget and added different display modes.

The display modes are CheckBox (like before) and Switch.
Used BoolWidget switch mode to improve CompoundDataPlugValueWidgets.

Fixes #65.
Merge pull request #584 from johnhaddon/hsvColorPicker

Added HSV readout for pixel below mouse in image viewer.
Merge pull request #585 from johnhaddon/pathFilterInputs

Allowed PathFilter paths plug to receive inputs.
Merge pull request #586 from johnhaddon/boolWidget

BoolWidget
Prevented rogue connections being made to Shader "parameters" Plug.

CompoundPlugs track the connections of their children, and connect themselves to match the child connections in the case that all children receive inputs from plugs which share the same parent. When connecting the output of an OSL node into the input of an OSL node with only a single parameter, this could lead to an unwanted connection being made to the top level parameters plug in addition to the wanted connection made to the child plug. Removing the AcceptsInputs flag on the parameters plug fixes the problem.
Merge pull request #589 from johnhaddon/rogueShaderParameterConnections

Prevented rogue connections being made to Shader "parameters" Plug.