Plugin template

Changes:

• migarted to freva-plugin-template
• divided shell script into multiple scripts (one for actual processing, one storing functions)
• setup functional testing
• added test data
• added basic informations to the output

Please have a look if the right licences were used and if any important part from the template is missing. The main objective for now was to get the plugin running using the freva-plugin-template. Additional improvements regarding code quality and input generalization will be done as soon as we switch to cmorized data.

Closes #1 (closed)