added another test case for bending_force_ibm
ifedfs for tcl callback functions of ibm and renamed stretching law callback in the header file
returned ibm methods to lb file, ifdef for lb force calculation in force_calc to work with ibm, commented wrong vecsub line in stretching_force_calc, renamed method to get_interpolated velocity for virtual sitesibm
decoupling of ibm logic from lb again after verifying it produces no problems
additions to ibm sample and tests
Merge branch 'master' into gpu

Conflicts:
	src/core/immersed-boundary/stretching_force_ibm.hpp
	src/core/immersed-boundary/virtual_sites_ibm.cpp
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