2. Add crop layer unitest
3. Fix bugs

For example:
layer.printer(input=[x, y], format="x=%s y=%s")

Also remove active_type argument for many layers in config_parser.py because it is automatically
handled by LayerBase.

No longer need to specify target_inlinks or is_seq.

No longer need to use SubsequenceInput. The framework will detect.

User can provide an initializer in ParamAttr. The initializer will be called when at parameters.create().