Issue 411: Pricing formulas

[veggiematts]

See Issue #411 for description.

Test plan:

• Apply the database update (resources/install/protected/3.0.0/005-411.sql (will move prior merging))
• Create a formula in resources admin -> pricing formulas
  
• Edit the cost history for a resource
• Check that the formula you created is available in the dropdown list
  
• Once the formula is selected, fill values for the formula, and click save
• Check that the payment amount is populated according to the formula values.
  

Once the cost informations are saved, the formula is displayed with its values on cost history edition.

[xsong9]

The Steering Committee reviewed the request and a couple of questions came up regarding the potential use. We'd love to discuss this with you at a future Steering Committee meeting.

[veggiematts]

Hi,

Sure, we'll try to be there at the next Coral SC meeting to answer your questions.

[veggiematts]

Any specific questions, by the way ?

[xsong9]

CORAL Steering Committee approved the PR.

[veggiematts]

Here are the requested modifications:

• Disable pricing formulas in acquisitions when no princing formulas are defined
• Add a sample formula when adding or editing a formula

Also, here is the paragraph to add in the documentation:
Pricing formulas are a good way to automatically calculate a price and to keep track of how said price has been calculated.

To add a pricing formula, go to the administration page in the resources module and click on the "Pricing Formula" tab.
Then, click on "add new formula". At the bottom of the screen, you will see an example of a simple pricing formula.

Here is another example:

Name: Multiple prices with two different discounts
Field 1: Price 1
Field 2: Price 2
Field 3: Price 3
Field 4: Price 4
Field 5: Discount 1
Field 6: Discount 2
Formula: (Price 1 + Price 2 + Price 3 + Price 4) * (1 - Discount 1 / 100) * (1 - Discount 2 / 100)

[veggiematts]

Hi ! Is anything still preventing this PR from being merged ?