Make Project and Plugin tasks extend BakeTask.

Using BakeTask as a base class will be required for bake to autodetect
tasks.
First pass at building task autodetection.
Add task discovery to BakeShell.

Bake will now autodiscover any tasks that subclass BakeTask and load the
as Tasks. This makes bake easier to extend and customize.

Refs #3249
Wire help and informational output to detected tasks.
Remove one of the interactive questions in plugin bake.

Bake is becoming less interactive as it makes the code less complex to
work with and easier to maintain/use (imo).
Update help text for several bake tasks.
Add test for option parser generation.
Fix failing tests.
Travis.ci ends up with differently ordered results than my computer does.
Merge pull request #3255 from markstory/3.0-bake-discover

3.0 bake auto-discover