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This patch removes the ktn/kti lists from most parts of the first half
of the loading sequence. Some remain as the [(String, Int)] is the
nicest way to lookup names and get indices back.

Since both nodes and instances support some common functionality (names
and indices), we add a class so that we can access these attributes in a
generic way.

In order to simplify the data structures, we add back the name on the
node and instance objects. We still keep the index for, well, indexing,
but we will use the name directly from the object, in order to get rid
of the ktn/kti arguments which are passed around everywhere.

This new big patch does a couple of more cleanups in the loading of data
chapter:
  - introduce a Types module that holds most types (except the base
    Node/Instance/etc.) so that multiple other modules can use these
    (instead of only Cluster and its users)
  - bring IAlloc.hs in line with the recent changes of providing data
    types and not strings
  - removal of obsolete Utils.hs json-related functions

This big patch changes the loader model from “string data as common
format” to actual object structures as common format.

The text loading function move from Cluster.hs to a new Text.hs module,
some common functions are moved to a new Loader.hs module, and the
return values from both Rapi.hs and Text.hs are uniformized.