-> configured the views filters to allow empty dates

- Field for countdowns for publishing as well as unpublishing
- Field option for scale (seconds, minutes, hours, days, weeks and a smart mode that selects the scale depending on the value)
- Field option for display of units (long units like '3 days', short units like '3d' or no units at all)

New hook: hook_scheduler_nid_list($action) - This hook gets called on scheduler cron run with an action (currently 'publish' and 'unpublish', not to be mistaken with action-modules actions) as parameter. scheduler expects modules to return a list of node IDs the module want published or unpublished respectively.

#988210 by plach and ericschaefer: Refactored the publishing and unpublishing code in hook_cron() out into separate functions

This refactoring is a preparation step for #988210:

- created _scheduler_publish() and _scheduler_unpublish()
- changed the code so that it would first gather an array of nids out of the query and then iterate over that array instead of iterating directly over the query result

#982258 by ericschaefer: Text under field needs to be changed for when unpublish schedule is a required field.

- Right now only eclipse .project files are ignored

#642018 by ericschaefer: 'a' and 'A' format characters do not work with date_popup (updated the format description)

#605648 by ericschaefer: 'G' format character does not work with date_popup (updated the format description)

#565298 by ericschaefer: googlebot and unavailable (lower case xhtml compatible tags and attributes)