Add first version of offer protobuf

This is just a first version. It just contains messages to discover
offers in the network. More messages have to be added in order to
provide messages to implement the exchange protocol.
Merge pull request #1 from apoloval/master

Add first version of offer protobuf
Added pom.xml and modules.
Merge pull request #2 from gotoalberto/master

Added pom.xml and modules
Add protobuf compilation
Add some classes for peer connection chains
Merge pull request #4 from apoloval/master

Add some classes for peer connection chains
Merge pull request #5 from sortega/server

Add protobuf compilation
Added definition to Payments Processors API.
Merge pull request #6 from gotoalberto/master

Added definition to Payments Processors API
Add server module and rpc definition
Merge pull request #7 from sortega/server

Add server module and rpc definition
Add registration message
Enable protobuf service code generation
Merge pull request #8 from sortega/server

Switch to protobuf 2.5.0 and enable service code generation
Add simple protobuf service server
Encapsulate protobuf service handling in common
Merge pull request #9 from sortega/server

Encapsulate protobuf service handling in common
Implemented OKPay stub module.
Change package and outer classname of proto

The package and the outer classname geneated from offer.proto are
causing name clashing with other classes. This change renames the
package to `com.bitwise.bitmarket.common.protocol.protobuf` and sets
the outer classname to `OfferProtocol`.