Viral load testing occurring too frequently in HIV module

[tdm32]

Viral load testing currently occurs at every follow-up appointment - if consumables are available.

Following Sakshi's analysis of costs, and Andrew's concerns about frequency of testing, we should reduce this to occur at most once a year.

This can be done by:

• maintaining VL testing at every follow-up but demanding 0.25 of the consumables per visit
• reducing frequency using probability 0.25 of test occurring per visit

For validation, output annual consumption of VL tests for comparison with costing data

[tdm32]

Noting also on here, related issue that malaria consumables quantities are not logged. This update has been made in the gf scenario branch and should be merged into master