Allow to add new "status" (like for the task app)

[ClemensRobbenhaar]

Currently the "status" field has only three hard wired options:

• open
• closed
• rejected

The proposal is to allwo users to add new status field like "in_review", "under_discussion" ,"postponed", "needs clarification" etc whatever. (Similar to the Tasks Application, which allows to add new entries for "Status" and "Priority", with some predefined values.)

[KebabRonin]

Hello, I have some questions about this feature:

• (IDEAS-48) Should the only selectable status for new pages be 'Open'? I could see custom statuses like 'Proposal' or 'In Review' challenging this rule.
• Should the order the statuses appear in be configurable? (If so, it would be nice to also fix application-taskmanager#177 as part of this implementation)
• Status categories for open poll and closed poll statuses?

[snazare]

to revisit once xwikisas/application-task#177 and xwikisas/application-task#180 are done