PEWImageView to minSdkVersion=7

Hi,
this is my simple modification to port PEWImageView to minSdkVersion=7 (I tested it on Gingerbread, API Level 10).
I fixed the wrong initialization of listeners:  they must be initialized / destroyed on onAttachedToWindow/ onDetachedFromWindow events, not in constructors.
If this PR is OK, you can change, in the same way, PEWTextView.
Bye