Make PlusLib reusable from other applications

[Sunderlandkyl]

Goal: Algorithms implemented in Plus should be reusable from Slicer modules or other external applications.

Approach: Modify PlusLib so it is usable alone. Compile PlusLib without hardware support.

Tasks:

• Try to compile PlusLib in a SlicerIGT module. Create superbuild CMake that checks out the code. (Andras)
• In the same module implement conversion between Plus tracked frame list and sequence nodes (Multidim Data). (Matt)
• Check how module/extension dependency works in Slicer so this module would automatically install Multidim Data. (Lower priority, Matt)

Migrated from https://app.assembla.com/spaces/plus/tickets/943/details

[adamrankin]

See https://github.com/IGSIO/IGSIO

[Sunderlandkyl]

@adamrankin Just FYI, I've already started migrating the updated TrackedFrameList from Plus to IGSIO.
I'll make pull requests once it's been migrated and the tests are passing.