Fix resource rates on cost estimator

[ianhinder]

In the cost estimator, https://balex.itservices.manchester.ac.uk/estimatecost, the "Resource rates" available for each task are

• Senior bottom
• Junior bottom
• Senior mid

The Leadership and RSE 1 tasks both default to "Senior bottom".

According to the Costing Policy,

• Leadership is costed at 7.8 (Senior top?), which is not available in the cost estimator list
• Development is costed at 7.5 (Senior mid) or 5.5 (Junior mid). The former should be the default, not "Senior bottom", and the latter is not available in the list.

My proposal:

• Include Senior top (7.8) in the list
• Include Junior mid (5.5) in the list
• Make the leadership task default to Senior top
• Make the development task default to Senior mid

[ianhinder]

PS: this means that it is not currently possible to use the cost estimator to cost a standard project, because "Senior top" (7.8) is not available to assign to the leadership task. Back to my spreadsheet!

[aharwood2]

Relates to #1410