The current (desired) behavior when a Command specifies a flag that
has the same name as a persistent/inherited flag, is that the local
definition takes precedence. This change updates the various
Flag subset functions to respect that behavior:
* LocalFlags: now returns only the set of flags and persistent flags
attached to the Command itself.
* InheritedFlags: now returns only the set of persistent flags inherited
from the Command's parent(s), excluding any that are overwritten by a
local flag.
* NonInheritedFlags: changed to an alias of LocalFlags.
* AllPersistentFlags: removed as not very useful; it returned the set
of all persistent flags attached to the Command and its parent(s).
Default UsageTemplate updated to use LocalFlags and InheritedFlags
