v0.4.0.beta2

#27 [v0.4.0] testing of build 0.4.0.v20180121-1352

new fixed issues in this build:

• impoved validator messages
• fixed some warnings
• added EMF mapping to 4.6 target platform
• improved validation of AttributeValue
  • moved check methods to ValidationUtil
  • added boolean validation
• update FM validation, so it checks wheter the default value is
  appropriate for the given attribute type
• Travis-CI: oraclejdk7 is not supported anymore (using openjdk8 and
  oraclejdk8 now)
• Updated default target platform to Oxygen (4.7) and added target
  platform for Eclipse Photon (4.8)
• Use Tycho 1.0.0 (removed openjdk7, because new Tycho (>=0.25)
  needs Java 8)