Module refactoring to be non-destructive and follow best-practices

Hi @jreinke, thanks for the great module. In this pull request I've done some refactoring that allows the module to be installed without overriding core template files or installing into a custom theme/package. The module templates have been moved to folders that correspond to the module's name (clevercms). This way all Clever CMS template files can be found in a single subfolder and not split up amongst other module's template files(catalog, page, customer, etc). Everything should still work out of the box and the custom top menu can be enabled by uncommenting a line in the layout xml.