make tools to color disconnectivity graphs

[js850]

The functionality is already there (it's already done in the gui), but we should make tools to color automatically via a calculated value. We should start by replicating what is done in disconnectionDPS

color minima by predefined groups:

! Colour minima in sections if required.
! For each node, check all minima for which the node is a parent.
! If all minima are contained on one of the lists, the node 
! will be coloured to represent that list.  
! If any minimum is not contained on one of the lists, the node
! is not coloured. 
! If all minima are contained on lists but more than one list 
! is represented, the node will be the colour of the last list
! as specified on the input line in dinfo.

This can be implemented by a function which takes a list of groups of minima as input.

Also, color minima by order parameter:

! Colour minima by value of DPMARKNODE, with input values in the range 0.0d0 to 1.0d0
! For each node, check all minima for which the node is a parent.
! The node will be the colour of the minimum with the highest value 

This can be implemented by a function which accept a function minimum_to_value as input