Support Spring Improvements & Bug Fixes

• Bug fix for cylindrical meshes.
• Added tension/compression only support springs. This required some reworking of how support springs are implemented. See the "Beam on Elastic Foundation" example for an example of how to properly use support springs.
• More PEP8 style changes. This shouldn't change the way you use the program. Some of the internal calls to function names still referenced the old function names. It was leading to deprecation warnings during runtime.
• Fixed a divide by zero error for plotting contours on models with nodes not attached to plates/quads.