[Plato] View plan analysis page read-only anytime

[christoph-becker]

Given the state model of preservation plans, it is sometimes not possible to view the information contained in the more advanced stages of preservation plans that are under revision, where their state has been reset by a save in a prior stage.
Say, a plan is COMPLETED, but then a word is added to the basis stage and it is saved. Given the checks that need to be done for verifying consistency, it is important that users need to progress again through the stages.
However, a great feature would be the introduction of a read-only variation of the plan analysis page, one that could be accessed with plans prior to that stage any time. It could be quite easily created based on the existing analysis page, adding a few checks on the presence of a plan, samples, alternatives, values, etc to ensure the page renders correctly in situations where the plan truly does not have a list of alternatives (for example).