Support creating new meteor app in current directory

Small change allowing this convenient method:

`meteor create .`

Uses 'helloApp' as the name for the app/files.

Has come up multiple times on google groups.  Mostly due to the fact that people create repo's online first (github), then `git clone` it locally and want to make it a Meteor app, which is not supported by the current 'create' command.

Most recent discussion: https://groups.google.com/forum/#!topic/meteor-core/1wlD_X3FoPc
Should rather be able to overwrite it with an optional parameter.
And have the name of the current by default of course.