Make control naming consistent

[verveerpj]

Is your feature request related to a problem? Please describe.
The variables that are optimized (controls in Everest nomenclature) are specified in a nested fashion: We have controls, which defines groups of variables, which in turn can have multiple components labeled with an integer index. For example (from config_advanced.yml):

controls:
  - name: point
    max: 1.0
    min: -1.0
    initial_guess: 0.25
    perturbation_magnitude: 0.005
    type: generic_control
    variables:
      - name: x
        index: 0
      - name: x
        index: 1
      - name: x
        index: 2

This defines three controls, with the following control, variable, and index fields:

• point, x, 0
• point, x, 1
• point, x, 2

When reporting results, control names are constructed from the three fields as follows control_variable-index, so we get:

• point_x-0
• point_x-1
• point_x-2

When specifying input constraints, weights need to be set for a sub-set of controls, so controls are needed, but in this case they follow the form control.variable-index. For instance (from config_advanced.yml):

input_constraints:
  - weights:
      point.x-0: 0
      point.x-1: 0
      point.x-2: 1
    upper_bound: 0.4

This is inconsistent and potentially confusing for the user.

Describe the solution you'd like
When a string representation of controls is shown, or required as an input, it should always have the same form. There should be a singe function/method responsible for formatting the string from control, variable, index fields. Preferably this transformation should be invertible, although we should not rely on that in code. If possible, the delimiters used should not be allowed in control and variable names. We should discuss the delimiters to use, but using . and - would be backwards compatible for specifying input constraints and it would leave the underscore available for control and variable naming.

[yngve-sk]

Do we need to have 2 delimiters for this? Why couldn't we just do point.x.0 for example?