Support receiver style syntax for given/when/then

[jangalinski]

Currently we are writing fluent method calls, as in java:

GIVEN
   .`a condition`()
   .AND
   .`another condition`()

WHEN
   .`something happens`()
THEN
   .`expect one result`()
   .AND
   .`expect second result`()

It would be more kotlin-link to use receivers and remove the .:

GIVEN {
   `a condition`()
   AND
   `another condition`()
}

WHEN {
   `something happens`()
}

THEN {
 `expect one result`()
  AND
  `expect second result`()
}