Financial NPV PWL - Githubissues

Addresses UR4 in #320.

See the implementation notes below:

By default, on first time load, the NPV configurations for all activities are disabled:

To enable the NPV for an activity, one should check the NPV Priority Weighting Layer group box:

The user should specify the number of years and discount, then enter the revenue and cost values for the respective years. The greyed out cells (i.e. Year and Discount Value) indicate that the values are automatically populated.
On updating the discount rate, revenue and cost values, the total NPV is automatically updated.
For an enabled NPV PWL, all revenue and cost values should be specified otherwise an error in the message bar will show which activity(ies) and corresponding years have missing values. This is shown when the user tries to create or update the PWLs.

It is recommended to leave the Use computed NPVs check box enabled - which is the default option - so that the minimum and maximum normalization values can be synced and automatically updated when the user input changes. The min/max values will be based on enabled NPV parameters for activities i.e. a disabled NPV (in the group box) will be excluded when computing the min/max normalization values.
When the Remove existing PWLs for disabled activity NPVs check box is enabled, any NPV PWLs that were previously created, will be deleted when updating the NPVs.
On clicking Update, a dialog showing the progress of creating/updating the NPVs will be shown.
On creating NPV PWL rasters, the corresponding PWLs will be created or updated in the list of PWLs. The naming convention is [activity name] NPV Norm:

An NPV layer, which is a constant raster containing the normalized value, will be created under the {BASE_DIR}/priority_layers/npv directory. The extents are based on the user extents defined in Step 1:

Editing of NPV PWLs is restricted to the description only as the name, layer and corresponding activity are managed through the NPV Manager Dialog:

ConservationInternational / cplus-plugin