* support rectangle padding, stride, window and input for PoolProjection

* Follow comments.
1. Remove start
2. refine img_pool_a/b.conf for test_NetworkCompare
3. Split unit test

* Modify the test in img_layers.py

* Fix lots of trainer_config_helpers bug, and complete unittest for `layers.py`

* add type compatible check for ParamAttr

* split dotmul_projection and dotmul_operator
* bug fix in outputsize checking for mixed layer

Sequences should be sorted according to the number of subsequences they have.

* Add some comments for CTC layer and fix CTC evalutors, also add interface test

Change cos_sim to use CosSimLayer layer when size=1 and rename convex_comb_layer to linear_comb_layer

Also add an unittest for layers.py, currently for a few things. More need to be added later.