Extracted all expression evaluation logic to CalculatorResource

I've tried to avoid modifying of xjc-generated classes in any way.
(Cause if there were thousands of them it'd be rather tedious)
So I moved all the logic responsible for calculating results to the
resource itself
Added maven JAXB plugin. Deleted generated sources

Now all classes are generated at build time
added target folder to .gitignore
Forgot about pom.xml!
Added JUnit in dependencies
Added simple unit tests. Thanks to them found and fixed bug in CalculatorResource
Added my tiny review of technologies used
Added test for zero division
Added message to error response and test for it.
Changed request body representation to InputStream
Finished WADL part of assignment

Added .wadl for restcalc service (taken from GET to restcalc:8000/application.wadl).
Added WADL and wadl-client-plugin in pom.xml (NOTE: wadl-client-plugin 1.1.3 is buggy!).
Updated tests to use generated client.