Add new Verify and Format Mojos in XAR plugin

And verify the following (and clean up automatically in the Format mojo):

• that the author/contentAuthor and creator are using xwiki:XWiki.Admin
• that a parent is set
• that the version is 1.1
• that the save comment is empty
• that minor edit is set to "false"
• that default language is empty
• that the encoding is UTF8

And add this goal in the XAR lifecycle so that it's called automatically for all projects using a packaging of "xar"

Rationale:

• Much faster to execute than using XMLRPC to remotely assert parents (what we are doing now)
• Provides faster failure
• Allow author of XARs to find their mistakes easily and to fix them