Tidying project compilation & ignore bin/debug

ILRepack is now included as a managed package
When compiling the project it:
- packages all binary files into a single .gha file using ILRepack and
moves it to the Grasshopper plugin library  (note: uses a hard-coded
path to plugin directory so is brittle)
- No longer attempts to register as a COM object
- Checks for integer overflow
- Does not attempt to open Rhino.

The bin and obj folders have been added to the gitignore.
GH_Beam now creates SharpFE 1DBeam

1DBeam replaces 3DBeam.
Updated SharpFE library dll

SharpFE library is updated.
GH_Node amended to use revised method signature (CreateForTruss is now
CreateFor2DTruss) in updated library.
Formatting whitespace in AssembleModelComponent
GenericCrossSection component added
Test Obj, Bin and Partcover now ignored

Ignoring built libraries within the Test project.
Minor refactoring of GH_Model

Removed redundant namespace path in method signature (the library is
called explicitly, so the namespace of the object can be implied.)
Merge pull request #1 from iainsproat/master

New GenericCrossSection type and general tidying