[WIP] Create cron run command

[alias-mac]

We have issues around 7.x version that needs discussion

Also, I think the new command options/arguments are better.

Support cron command like we had on version 1.0.

$ insulin help cron-run
Run system cron jobs.
Examples:
 insulin cron-run Runs all active jobs who are able to be executed according to their last 
run time.
 insulin cron-run --force Runs all jobs without checking last run time.
 insulin cron-run --jobs=1,2,3 Runs cron for job with Ids 1, 2 and 3.
Options:
 --jobs A comma delimited list of job ids.
 --force Force jobs to run without checking last run time.

[alias-mac]

We should add documentation about this document using the template (https://github.com/insulin/cli/wiki/Command-Specification-Template).

[coveralls]

Coverage decreased (-1.96%) when pulling 28298c9 on alias-mac:ticket-50 into 5715b6c on insulin:master.

[jcsmorais]

Why not doing BeanFactory::getBean('Schedulers'); instead?