Fix leading space for issue and mr formats on default project

This patch allows zero leading space format for issue and mr command on default project (ghc/ghc), as following:

• issue 1
• mr 1

Currently, a leading space is required on default project, like this:

ghci> parse parseQuery "query string" " issue 1"
Right (IssueQuery Nothing 1)

ghci> parse parseQuery "query string" "issue 1"
Right (SearchQuery Nothing "issue 1")

The latter don't generate IssueQuery command.

This patch splits IssueQuery into two formats: default project and explicit project.

Please modify or drop this patch for your concept. Thanks for useful service.