Add new mode "lint"

[tbrowder]

Do at least the following:

• ensure META6.json lists all dependencies
• ensure META6.json lists all modules provided
• ensure resources are handled properly
• ensure ALL modules are load tested, e.g., use-ok("My::Module")

Ideally, the above would be done by App::Mi6

[tbrowder]

Also consider new option to add a separate module to provide resources handling (just the subs).