#6 Subproject feature

[Andreas Schwarzkopf]

When processes become slightly more complex, filter boards become unoverseeable. Things get out of focus. On the other side it can appear that users put same redundant filter groups which make an additional effort. So there can be a sense to provide some modularity.

Main features:
- Allowing projects to be imported as modules
- Another two plugins to export input and output connectors of a project to use them in its parent project
- Proposed to support subprojects with an arbitrary depth