Load plugins in a given position

[ray-millward-tessella]

Description
By this point we should be loading plugins from config, now we need to add another field to the config to specify the position in the app. The exact set of locations needs to be specified but for the purpose of this story could be simple to prove the mechanism works (in the future this will most likely be placed inside tabs)

Acceptance criteria:

• There is a position field in the config for plugins
• Plugins are loaded in to the right position when the app starts