templates: rewording of VM validation instructions

* Rewords VM validation instructions.  (closes #177) (PR #188)
templates: propagation of "selection" information

* Propagates "selection" metadata information (taken from JSON field
  `methodology_note` aka MARC tag `567`) into various detailed record
  page templates.  (addresses #120)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: propagation of "validation" information

* Propagates "validation" metadata information (taken from JSON field
  `action_note` aka MARC tag `583`) into various detailed record page
  templates.  (addresses #120)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
templates: propagation of "usage" information

* Propagates "usage" metadata information (taken from JSON field
  `constituent_unit_entry` aka MARC tag `774`) into various detailed
  record page templates.  (addresses #120)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
UI: remove account traces

* (addresses #44)
UI: file list + preview added - "PrimaryDataset"

* preview functionality added for “.txt” files