Enhancement: concentrate crossover session handling in one function, Fix: crossover session device cleanup. (Issue reported by Ian McAlees)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5643 43c1dc8c-776e-4df2-8ef1-6e829299be21
Fix: Handle buttons with a type but without any options as an empty button. (Issue reported by Dave Burgess)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5644 43c1dc8c-776e-4df2-8ef1-6e829299be21