change relevant fields to text or big varchar

Change relevant fields (i.e. name) to text or a big
character varying limit (i.e. 4096 for paths), for
the following tables:

  - entities
  - categories
  - formalitylevels
  - licensemodels
  - links
  - logics
  - languages
  - metadata
  - ontologies
  - ontology_types
  - ontology versions
  - oops responses
  - projects
  - repositories
  - resources
  - sentences
  - serializations
  - tasks
  - teams
  - tools
  - url maps
  - users

As requested these changes are applied into one massive
migration. This also includes the necessary adjustments
to model-column based tests.
add test for not displaying mapped symbols

If a symbol A is mapped to another symbol B, we should
not display (or actually register) symbol A for the
ontology to which the mapping is applied.
ensure non-exec of symbol callback in link

When in a symbol-mapping link (DGLink which contains
a map element) we should not execute the callback
for a symbol, as this will create the symbol
as part of the current ontology. And this not really
what we want.

Oh by the way: The spec is green.
add spec for ext-references in DOs

If a single ontology in a distributed ontology references (i.e. imports)
an ontology which is not part of the distributed ontology, the
link/mapping should be created correctly and without failure.
support references in distributed ontologies

distributed ontologies (actually single ontologies in distributed
ontologies) can also import and reference ontologies which are not part
of the distributed ontology. So we cannot use `iri_for_child` to infer
the ontology-iri on ontohub for a referenced DGNode name. Instead we
create an ontology aliasing map which maps DGNode names to their
corresponding ontology-iri, which is determined when creating/finding
the specific ontologies.

This leverages the fact that DGLinks are always placed after the
DGNodes in hets-xml output.
use hets-xml fixture to not trigger remote network

In order to not use a remote network connection to
find the referenced ontology, we (sadly) need to
use a hets-xml output fixture.
Merge branch 'staging' into 765-references_in_distributed_ontologies
Merge pull request #823 from ontohub/767-avoid_symbol_creation_caused_by_mapping

767 avoid symbol creation caused by mapping
Merge pull request #811 from ontohub/534-adjust_possible_overlength_text_fields

534 adjust possible overlength text fields
remove unused message css class
Merge pull request #832 from ontohub/300-compact_history_view

make commits list more compact
Merge pull request #810 from ontohub/765-references_in_distributed_ontologies

765 references in distributed ontologies
Merge pull request #841 from ontohub/hotfix-check_proper_request

improve decision for html or plain text sending of file
Merge branch 'staging' into develop