Multiple link surrounds

Currently the definition of french drains requires the following steps:

1. Add a node number under storage

2. Select 'Link Surround' under structure type

3. Input of data (coefficients, safety factor, porosity, Link number, surround shape, diameter)

This is labour intensive, especially in the case of multiple links being french drains. It would be easier if a table (similar to Nodes and Links definition) was used, in order to copy-paste from Excel.