Header, cookie, and form parameters should be optional

According to the spec
(https://github.com/wordnik/swagger-spec/blob/master/versions/2.0.md#parameterObject),
only "path" parameters are required by default, while for
all other parameter types the default value is "false".
Header, cookie, and form parameters should be optional

Unittests fixed

Conflicts:
	modules/swagger-core/src/test/scala/parameter/ParameterSerializationTest.scala
Java 8 compile fix

Compilation with Java 8 had failed:
reference to Parameter is ambiguous.
both class java.lang.reflect.Parameter in java.lang.reflect
and interface com.wordnik.swagger.models.parameters.Parameter in com.wordnik.swagger.models.parameters match
renamed and added tests per #766
Merge remote-tracking branch 'upstream/develop_2.0' into develop_2.0_interfaces
Merge pull request #725 from martoe/params_optional

Fixed the default value for the "required" flag of header-, cookie-, and form-parameters
Add support for readOnly field in properties. Initialize description and defaultfields of properties if present when deserializing from JSON.
Merge remote-tracking branch 'upstream/develop_2.0' into develop_2.0_interfaces
updated property access
added tests
Merge branch 'develop_2.0' of github.com:swagger-api/swagger-core into develop_2.0
Merge pull request #734 from martoe/java8

Java 8 compile fix
Merge pull request #779 from mbarbanson/develop_2.0_interfaces

Develop 2.0 interfaces
Merge branch 'develop_2.0' into develop_2.0_interfaces