Use consistent prefix to label WMS-only attribute columns

[robbibt]

Currently a number of columns in the rates of change statistics file are included only for the purpose of ordering and labelling the data in the WMS, and do not need to be included in the data package itself:

• abs_time
• retreat
• growth
• conf_time
• conf_soi

To seperate these columns from others so it's clear they are used for web services only, these columns could be renamed consistently like

• wms_abtime
• wms_retr
• wms_grow
• wms_ctime
• wms_csoi

[robbibt]

Done