use Blob directly instead of shared_ptr for ConvolutionLayer::bias_multiplier_

This will make layer reshaping easier and more uniform, and is
consistent with col_buffer_.
use Blob directly instead of shared_ptr for InnerProductLayer::bias_multiplier_
use Blob directly instead of shared_ptr for PoolingLayer::max_idx_

Again, this is more uniform, and will simplify the implementation of
Reshape.
use Blob directly instead of shared_ptr for DropoutLayer::rand_vec_

This will simplify the implementation of Reshape by making allocation
automatic. There is no need for shared_ptr here, and this is more
uniform with buffers used by other layers.
use Blob directly instead of shared_ptr for DataLayer buffers
use Blob directly instead of shared_ptr for ImageDataLayer buffers
use Blob directly instead of shared_ptr for WindowDataLayer buffers
Merge pull request #742 from longjon/direct-blob-buffers

Use Blob directly instead of shared_ptr for internal layer buffers