Add build scripts -- fail the build if swagger-ui has not been initialized

Added .sh and .bat flavors of a root-level build project.  When building Swashbuckle with either the scripts or Visual Studio, if git submodules have not been initialized, fail the build.

Might be a more definitive way to know if this has been done, but the symptom typically is that when you go to use swagger, an exception that an embedded resource named "index.html" cannot be found.