Add monocot pipelines

[talmo]

In #51, we defined a new Pipeline base class and the DicotPipeline subclass which derives from it and implements the trait pipeline for dicot traits.

We now need to implement monocot pipelines which implement the specific logic for young and mature monocots.

These should implemented the define_traits and get_initial_frame_traits methods appropriately, including setting the appropriate monocot flags for individual trait computation functions, skipping traits that aren't used for those species, and dealing with renaming or missing lateral/primary/main root types.

[eberrigan]

This issue has been resolved by the merged pull request #54 . Closing this issue now.