[chronos-sync] Validate fields, use defaults.

The required fields should be validated, and we should set a default for
some optional fields (only `highPriority` at this point).
Adding softError property to Job entity

It will be used to control whether a job failure should or should not short circuit it's dependency graph.
Don't schedule queued jobs if they have been disabled
Remove a meaningless function invoking

Invoking skipForwad is not needed if job.schedule cannot be parsed.
So it is meaningless to parse it twice.
Extracts processDependencies and applies it to failed jobs if softError is enabled
Test coverage for softError feature

Testing that the field gets persisted and that it works as expected in the integration tests.
Merge pull request #303 from meelapshah/master

Don't schedule queued jobs if they have been disabled
Merge pull request #306 from depay/master

Remove a meaningless function invoking
Change type of disk and mem from int to double

Disk and mem in resources from Mesos are double but not integer.
Using integer may lead resouce in mesos becoming some number
like 1.0*e-15 instead of 0.
Indentation fixes
Merge pull request #308 from depay/master

Change type of disk and mem from int to double
Fix: task isn't removed from zk when failure hanppens

Persisting the old taskId but not the new one when handling failed task
causes the problem.
Merge pull request #309 from depay/master

Fix: task isn't removed from zk when failure hanppens
Merge pull request #307 from uken/soft-errors

Soft errors
Adding support for Slack notifications
Merge pull request #310 from motusllc/slack-notifications

Adding support for Slack notifications
Adding Mesos slave hostname to environment
Merge pull request #311 from motusllc/hostname_envvar

Adding Mesos slave hostname to environment
Merge pull request #261 from airbnb/chronos-sync

[chronos-sync] Validate fields, use defaults.
Improve run interval description

README.md modified based on the discussion at https://github.com/airbnb/chronos/issues/313