Pagination for schedules

Added the pagination capability to the v1/schedules api to support
limit and markers. It has limit_param_default and api_limit_max config
params to enable constrained limiting. Also, added unit tests for the
changes made.

Some important changes to be noticed:-
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1. simple db now does not generate id-s for schedules
2. id-s are being provided into the fixtures for the tests to be aware
   of them
3. validation of limit does not accept '0' as a limit (unlike glance)
4. schedules_mutate list is being used as a sorted one in the
   pagination module (does not add sorting feature but sorts the list
   chronologically using 'id' as a key)
5. there are 4 UUIDs set as default in the test_schedules module, and
   UUID_test can be set a custom UUID for tests that need it
Worker pagination wip
Pagination jobs wip