reapply namespace change
Merge pull request #752 from Yangqing/sweep

reapply namespace change
Add phase, level, and stage to LayerParameter to define when each layer
will be used.
Incorporate net, net_param, level, stage into Solver/Net.
FilterParam method called from Net::Init excludes layers that the
user specified shouldn't be included in the current phase, level, or
stage.
Use unified train/test nets in examples.
Move phase/level/stage into a "NetState" message, and filtering rules
used in Layers into a "NetStateRule" message.
Rewrite Net::FilterParam with refactored proto fields.
Add INPUT layer so deploy nets can be incorporated as well.
Fix examples to use new NetState/NetStateRule proto messages.