Start Helper bake task.
Extract SimpleBakeTask

HelperTask and BehaviorTask were so similar that their differences could
be expressed as simple set of properties.
Update other bake tasks to use newer style path generation.

Fix incorrect help text.
Hook helper task into BakeShell.
Add template and task for component generation.
Collapse Helper and Behavior task tests together.

These classes have all their code defined in the super class, so there
is no reason to maintain double the test cases.
Use an abstract class instead of public properties.

Having an abstract class will make the bake task collector much simpler
as it we can detect base classes like SimpleBakeTask. Having methods
means implementations could use custom code if they wanted.
Add additional imports people are likely to need.
Wire component bake into BakeShell.

Fix merge conflict mistakes.
Add default config properties to generated classes.
Merge pull request #3240 from cakephp/3.0-helper-bake

3.0 Add helper & component bake