* Make float equal works well.
  * compare 0.01 and 0.009999999999 will return true.

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

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.