Rename category to perm_link on measurement_type

Also don’t allow non-root systems to change the perm_link once it’s set.
Allow filtering on partial perm_link

GR-57
Merge pull request #28 from CruGlobal/GR-29__GR-57

GR-29  and GR-57
Fix filtering measurements on related_entity_id.

Included spec for regression testing
Add gt, lt, gte, lte filters
Merge pull request #30 from CruGlobal/GR-64__gt_lt_filters

Add gt, lt, gte, lte filters
db:schema:load and :seed instead of just migration

by replacing db:migrate with db:setup
Reduce .memory and .cpus
Merge pull request #31 from CruGlobal/db_seed_in_vagrantfile

db:seed in Vagrantfile  / also, reduce VM .memory and .cpus
Fix nil issue on filter
Merge pull request #32 from CruGlobal/fix_nil_error_on_measurement_type_filter

Fix nil issue on filter
Passed on the owned_by filter to the related entities, when seriealizing a relatioship entity.
I am having problems running specs in my local environment - so I do not have a spec for this yet - but I have manually tested the fix.
improved code style
somehow a wierd character got added!
Made a couple of lines shorter...
Added spec
Formatted to please rubocop!
Merge pull request #33 from CruGlobal/GR-58__consistently_show_related_entities

Gr 58  consistently show related entities
Use local Dockerfile to build global_registry
Add merge functionality (with notifications)