Enable Grouping

[gigjozsa]

Enable the user to define a group, a list of which should appear in a box.

Implement two buttons, group and ungroup.

A group should be defined by clicking on one data point, then clicking on Ctrl and another point and so on. When this is being done the parameters should be highlighted in the plot. If one clicks multiple times on a data point the highlighting will be switched on and off alternatingly. By clicking on group, a group #i (i integer) containing the highlighted data points is defined.

Once the user klicks on a group listed in the panel that group should be highlighted and activated. Once activated an action on one data point in the group (shifting up and down) should affect all data points in that group simultaneously.

If one wants to remove a group, the user should click on the group in the group panel and on ungroup. Data points can be added to a group by activating the group and using ctrl (and shift) again.

If one wants to highlight (add to the group) many parameters in one go, the shift key should be usable to highlight all data points between an already active one and the one that you click then.

Also, it should be possible to highlight a group of parameters by dragging a box around the parameters belonging to the group.

[gigjozsa]

This needs to be reviewed.

[gigjozsa]

This should probably be different from fitting groups (the group definition that determines the VARY= input), but the technique can be the same.
There should be a mechanism to activate single data points and groups for fitting. But that later.