* fix primary key changing on upsert, fix#342
* add 'update_columns' in 'on_conflict' object, consider 'allowUpsert'
* 'ConflictCtx' type should respect upsert cases
* validation for not null fields in an object
* don't allow fkey based relations from/to a table that isn't tracked, fix#185
Check if remote table exist in metadata when creating foreign-key
based object relationship.
* add tests for adding object relation using fkey if remote table is untracked
* filter schema identifiers to conform to graphql naming scheme,closes #134
Filter out tables, columns, relationships etc which does not conform to
graphql naming scheme.
This ensures GraphiQL initialisation works properly for existing
databases.
* rename `isGraphQLConform` to `isValidName`
* rename all graphQL validators
* add 'on_conflict' condition to allow upsert mutation, closes#105
* check for empty unique or primary key constraints
* add 'on_conflict' condition test cases and introspection test case
* update 'conflict_action' enum values' description
* server: basic test setup
* server: use the default transaction mode
* server: basic tests in yaml files
* server: restructure test setup and some more tests
