Allow admins to setup custom placeholder text in free-text fields.

Request:
Allow Jira administrators, to configure custom placeholder text to appear in free-text issue fields (Summary, Description, custom free text fields), on a project-by-project basis.

Benefits:

• Team members receive constant non-intrusive guidance, on how best to use certain fields, every time they create an issue. e.g. teams using Gherkin syntax for Stories, could be reminded of this by 'As...When...Then' placeholder text in Summary field.
• Different teams working on different projects retain flexibility to follow their different processes.
• Non-intrusive way to remind team members to follow chosen conventions/best practices.
• Placeholder text is better than default text, as it doesn't require deleting or editing of default text. Team members can just click/tab into fields and immediately start typing.
• Allows admins to also offer guidance on use of fields such as Summary, and other project-specific custom free-text fields.

This request is not the same as http://jira.atlassian.com/browse/JRA-4812 because:

• Placeholder text is better than default text, as it doesn't require deleting or editing of default text.
• This request is for all free-text fields, not just Description.