Coding guidelines for plugin and client development

[christiangessner]

create coding guidelines for

• Plugin services and property names (to make clients and plugins compatible)
• Plugin guidelines in general (which code in which cs files: services, entities, werbservice etc.)
• Client coding guidelines similar to what the project team has as general coding guidelines. E.g. syntax, variable naming, etc.)
• Client file description (which code belongs in which file)