Assign categories to scripts so they are easier to search and browse

Assignment of categories to scripts should increase their usability as scriptler becomes more pervasive in the Jenkins build environment. Scriptler build steps would be first selected from a category that would then allow selection of a specific script in the category. In my work using Jenkins in life science applications scriptler scripts can represent distinct and modular computational steps and having them categorized greatly helps in identifying and selecting the right build step script.