New feature: Variable width transects

[jrutyna]

A new feature should be developed that allows the user to create variable width transects that would allow the create polygon tool to create model segments that are more tailored to the user's preferred model domain. One possible way @jrutyna thought could work would be to have another optional input shape file polygon layer of the model domain and have QGIS extend/trim the transects to the intersection of the this polygon model domain polygon... the details of the geoprocessing would need to be worked out.